Multiplex communication system and method

ABSTRACT

Disclosed are the multiplex communication system and the method therefore. A fault detection part of a duplex switching device detects it as generation of fault when recognizable signals are not detected from a connected line within a prescribed time. When the fault detection part detects the generation of fault in the present system line, the line switching part switches the lines from the present line to the standby line to perform communication between a terminal device and another terminal device therethrough. Also, the fault detection part notifies the generation of fault to the other duplex switching device after a prescribed switching protection time has passed from the time of the fault detected by the fault detection part, so the selection of the lines becomes consistent.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a line switching system, anoptical transmission switching device, a multiplex system and anEthernet redundant method and the system, which are best applicable to amultiplex communication, specifically, to communication using Ethernet®.

[0003] 2. Description of the Related Art

[0004] When achieving the multiplex communication, a line switchingsystem is employed in which a plurality of lines are provided within thecommunication system and switching of the line (communication path) tobe used is performed when, for example, a communication fault isgenerated in some part of the line.

[0005] As an example of a conventional data transmission system, thereis a system comprising, in order to improve the reliability of thetransmission, a present system line which is regularly used forcommunication and the standby system line, in which the line is switchedto be used for the communication.

[0006] For example, a transmission system using Ether frame is lessexpensive compared to SONET/SDH (Synchronous Optical Network/SynchronousDigital Hierarchy) and has been largely used for LAN. The capacity ofthe transmission suing the Ether frame has been increased to meet theneed of the times and the transmission capacity by one line has beenrapidly increasing. Generation of a fault in such interface meansinterrupting a large amount of data so that the damage is enormous. In anetwork built by using a router, in general, there is a method in whichthe transmission path is switched by using a routing protocol when thereis a fault.

[0007] A wavelength multiplex optical communication system disclosed inJapanese Patent Application Laid-open No. 11-50551 applied earlier bythe applicant of this application comprises: as a present opticaltransmission system and a standby optical transmission system, anoptical transmission system, respectively, in which a wavelengthmultiplex optical communication device having a transmission part and areception part of wavelength multiplex signal light is placed through anoptical transmission line. The reception part of the wavelengthmultiplex optical communication device comprises an alarm circuit foroutputting an alarm signal when the signal light is not normallyreceived, and an attenuator for attenuating the wavelength multiplexsignal light when receiving the alarm signal outputted from the alarmcircuit.

[0008] Thereby, all the light signals which are wavelength-multiplexedare automatically switched to the other transmission path so that it ispossible to achieve maintenance and restoration work more rapidlycompared to that of the related art.

[0009] However, in the above-described conventional system in which thetransmission path is switched using the routing protocol, it requiresrerouting of the lines to the other line by a router or the like. Thus,it takes an incredibly longer time from the detection of a fault to thecompletion of switching compared to a duplex switching by a protocolwith a function of switching the lines such as SONET/SDH. Therefore, anenormous amount of notification is o be lost during the time.

[0010] If there is a switching system as that in SONET/SDH to be appliedat the point of transmitting the Ether frame, however, there is no suchsystem in the standard of Ethernet®. That is, in the case of achievingcommunication using a protocol without the function of switching thelines, it is time-consuming to perform duplex switching. Further, if anew protocol is provided to achieve this, it becomes incompatible inregards to interface.

[0011] A subject has been raised on how to achieve duplication of theline in the interface having no duplex switching protocol withoutchanging a basic protocol in a network device. By defining a newprotocol and terminating at a switching point, the interface becomesincompatible and the specification needs to be changed by each device.Further, by terminating the protocol, the device becomes complicatedthereby increasing the price.

[0012] Further, the wavelength multiplex optical communication systemdisclosed in Japanese Patent Application No. 11-150511 utilizes theline-switching function of the protocol so that it is not applicable tothe protocol with no line-switching function.

[0013] Furthermore, conventionally, there are also problems in regardsto an optical transmission switching device, a multiplex system, andEthernet system, respectively, used in a multiplex communication.

SUMMARY OF THE INVENTION

[0014] A first object of the present invention is to provide a lineswitching system and the method, which can achieve switching of lines ata high-speed even in a system in which communication is achieved using aprotocol without a switching function of lines without adding expensivehardware.

[0015] A second object of the present invention is to provide a lineswitching system and the method, which can achieve switching of lines ata high-speed even in a system in which communication is achieved using aprotocol without a switching function of lines without changing thebasic protocol in the network.

[0016] Further, a third object of the present invention is to provide anoptical transmission switching device, a multiplex system, an Ethernetredundant method and the system, which are best applicable to amultiplex communication.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a block diagram showing an example of the configurationof a line switching system according to an embodiment of the presentinvention;

[0018]FIG. 2 is a block diagram showing an example of the configurationof a duplex switching device (a line switching device) of the lineswitching system;

[0019]FIG. 3 is a block diagram showing an example of the outline of analarm transfer method when a fault is generated in a line 105 c in theline switching system;

[0020]FIG. 4 is a waveform chart for describing the relations between atransmission delay time, output interruption time, and a link downpattern transmission time in the line switching system;

[0021]FIG. 5 is a block diagram showing an example of the outline of analarm transfer method when a fault is generated in a line 105 g in theline switching system;

[0022]FIG. 6 is a block diagram showing an example of the outline of analarm transfer method when a fault is generated in a line 105 m in theline switching system;

[0023]FIG. 7 is a block diagram showing an example of the outline of analarm transfer method when a fault is generated in a line 105 a in theline switching system;

[0024]FIG. 8 is a block diagram showing an example of the outline of analarm transfer method when a fault is generated in a line 105 b in theline switching system;

[0025]FIG. 9 is an illustration showing an example of transmission datafrom each device to a connected line at the time of the alarm transfershown in FIG. 3;

[0026]FIG. 10 is an illustration showing an example of transmission datafrom each device to a connected line at the time of the alarm transfershown in FIG. 5;

[0027]FIG. 11 is an illustration showing an example of transmission datafrom each device to a connected line at the time of the alarm transfershown in FIG. 6;

[0028]FIG. 12 is a block diagram showing an example of the configurationof a line switching system according to another embodiment of thepresent invention;

[0029]FIG. 13 is an illustration showing the outline (an image) of theconnection in a line switching operation of the line switching systemshown in FIG. 12;

[0030]FIG. 14 is a block diagram showing the configuration of an opticaltransmission system according to the embodiment of the presentinvention;

[0031]FIG. 15 is a block diagram showing the configuration of amulti-rate switching device (transmission side) shown in FIG. 14;

[0032]FIG. 16 is a block diagram showing the configuration of amulti-rate switching device (reception side) shown in FIG. 14;

[0033]FIG. 17 is a flowchart showing a method for setting the rate ofinterface;

[0034]FIG. 18 is an illustration showing a table of SFP interface types;

[0035]FIG. 19 is an illustration showing a table of SFP transmissioncode types;

[0036]FIG. 20 is a block diagram showing the configuration of anotheroptical transmission system according to the embodiment of the presentinvention;

[0037]FIG. 21 is a block diagram showing the configuration of amulti-rate switching device (transmission side) shown in FIG. 1;

[0038]FIG. 22 is a block diagram showing the configuration of amulti-rate switching device (reception side) shown in FIG. 1;

[0039]FIG. 23 is a block diagram showing the configuration of amultiplex system according to an embodiment of the present invention;

[0040]FIG. 24 is a block diagram showing the configuration of amultiplex system according to the embodiment of the present invention;

[0041]FIG. 25 is a block diagram showing the configuration of amultiplex system according to the embodiment of the present invention;

[0042]FIG. 26 is a block diagram showing the configuration of anothermultiplex system according to the embodiment of the present invention;

[0043]FIG. 27 is a block diagram showing the configuration of themultiplex system according to the embodiment of the present invention;

[0044]FIG. 28 is a block diagram showing the configuration of themultiplex system according to the embodiment of the present invention;

[0045]FIG. 29 is a block diagram showing the configuration of stillanother multiplex system according to the embodiment of the presentinvention;

[0046]FIG. 30 is a block diagram showing the configuration of the stillanother multiplex system according to the embodiment of the presentinvention;

[0047]FIG. 31 is a block diagram showing the configuration of the stillanother multiplex system according to the embodiment of the presentinvention;

[0048]FIG. 32 is a block diagram showing the configuration of an Exampleof a communication system according to the present invention;

[0049]FIG. 33 is a block diagram showing the configuration of the duplexdevice shown in FIG. 32;

[0050]FIG. 34 is a block diagram showing the configuration of anotherExample of the duplex device shown in FIG. 32;

[0051]FIG. 35 is a block diagram showing the configuration of aconventional optical transmission system;

[0052]FIG. 36 is a block diagram showing a conventional opticaltransmission system in which a duplex structure is employed; and

[0053]FIG. 37 is a block diagram showing the configuration of aconventional duplex device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] First, a line switching system in a multiples communicationsystem according to the present invention will be described. The lineswitching system comprises a plurality of terminal devices and aplurality of line switching devices. In the system, at least oneterminal device is connected to one line switching device and one lineswitching device is connected to another line switching device via apresent line (line used for the present communication) and a standbyline (standby system line), and one terminal device is connected toanother terminal device prescribed beforehand to be capable ofcommunication via a line switching device and a present line so thatcommunication is achieved using a protocol without a line switchingfunction. The standby line is a line replaceable with the present line.The line switching device of the system comprises: a fault detectionunit for detecting generation of a fault through checking whether or nota recognizable signal is detected from a line within a prescribed time;and a line switching unit for, when the fault detection unit detectsgeneration of a fault in the present line, switching the present linewith the fault detected by the fault detection unit to the standby linewhich can be replaced with the present line thereby to performcommunication between the terminal device and another terminal deviceprescribed beforehand.

[0055] It is desirable that the line switching unit switches the lineafter a switching protection time has passed from the detection of afault by the fault detection unit.

[0056] Further, it is desirable to comprise a fault notification unitfor notifying generation of fault to another line switching device whenthe generation of fault is detected in the fault detection unit.

[0057] Also, the lines used for connecting each device are full duplexlines (line achieved by full-duplex system) composed of a transmissionline and a reception line. The fault notification unit may comprise: afunction of, when a fault is detected in one of the lines out of thefull duplex lines by the fault detection unit, notifying the fault usingthe other line of the full duplex lines.

[0058] Further, the fault notification unit may comprise a function ofnotifying a fault by periodically repeating interruption of signaloutput and transmission of a link down pattern for downing the link in aprotocol. Also, in a period in the periodical repeat, time fortransmitting the link down pattern may be set longer than time forinterrupting output.

[0059] Further, it may comprise at least one transmission device capableof achieving a long distance communication between a terminal device andanother terminal device, which is provided in each of the present lineand the standby line in a line switching device. Also the transmissiondevice may comprise: a transmission-side fault detection unit fordetecting generation of a fault when a recognizable signal is notdetected from the line within a prescribed time or by receivingnotification of a fault generation; and a transmission-side faultnotification unit for notifying the generation of fault when thetransmission-side fault detection unit detects the generation of fault.

[0060] Also, the transmission-side notification unit may have a functionof: notifying the generation of fault to a line switching device byinterrupting signal output; and notifying for a transmission device byperiodically transmitting a reception fault notification packet and alink down notification packet. Also, in a period in the periodicaltransmission of the notification, time for transmitting the link downnotification packet maybe set longer than time for transmitting thereception fault notification packet.

[0061] Further, the detection of a fault through receiving notificationof the fault generation transmitted from the transmission-side faultdetection unit may be achieved by receiving the reception faultnotification packet or/and receiving a link down notification packet.

[0062] Also, when the fault detection unit detects a fault generated inbetween a terminal device and a line switching device nearest to theterminal device, the fault notification unit may transmit a link downpattern to a transmission line.

[0063] In a line switching method for performing line switching in amultiplex communication system, at least one terminal device isconnected to one line switching device and one line switching device isconnected to another line switching device via a present line and astandby line; one terminal device is connected to another terminaldevice prescribed beforehand to be capable of communication via a lineswitching device and a present line so that communication is achievedusing a protocol without a line switching function; and the standby lineis a line replaceable with the present line. The method comprises: afault detection step for detecting generation of a fault throughchecking whether or not a recognizable signal is detected from a linewithin a prescribed time; and a line switching step for, when the faultdetection unit detects generation of a fault in the present line,switching the present line with the fault detected by the faultdetection unit to the standby line which can be replaced with thepresent line thereby to perform communication between the terminaldevice and another terminal device prescribed beforehand.

[0064] In the line switching step, it is desirable that the line isswitched after a switching protection time has passed from the detectionof a fault by the fault detection unit.

[0065] Also, it is desirable that the method further comprises a faultnotification step for notifying generation of a fault to another lineswitching device when the generation of a fault is detected in the faultdetection unit.

[0066] Further, the lines used for connecting each device may be fullduplex lines (line achieved by full-duplex system) composed of atransmission line and a reception line. Also, in the fault notificationstep, when a fault is detected in one of the lines out of the fullduplex lines by the fault detection step, the fault may be notifiedusing the other line of the full duplex lines.

[0067] Further, it is desirable that, in the fault notification step, afault may notified by periodically repeating interruption of signaloutput and transmission of a link down pattern for downing the link in aprotocol; and in a period in the periodical repeat, time fortransmitting the link down pattern may be set longer than time forinterrupting output.

[0068] Further, at least one transmission device capable of achieving along distance communication between a terminal device and anotherterminal device may be further provided in each of the present line andthe standby line in a line switching device. Also, the method maycomprise a transmission-side fault detection step for detectinggeneration of a fault by the transmission device when a recognizablesignal is not detected from the line within a prescribed time or byreceiving a notification of a fault generation; and a transmission-sidefault notification step for notifying the generation of fault when thegeneration of fault is detected in the transmission-side fault detectionstep.

[0069] In the transmission-side fault notification step, a lineswitching device may be notified by interruption of signal output; and atransmission device may notified by periodical transmission of areception fault notification packet and a link down notification packet.In a period in the periodical transmission of notification, time fortransmitting the link down notification packet may be set longer thantime for transmitting the reception fault notification packet.

[0070] The detection of a fault through receiving notification of thefault generation in the transmission-side fault detection step may beachieved by receiving the reception fault notification packet or/andreceiving a link down notification packet.

[0071] Further, when a fault generated in between a terminal device anda line switching device nearest to the terminal device is detected inthe fault detection step, a link down pattern may be transmitted to atransmission line in the fault notification step.

[0072] Next, a specific example of the line switching system and themethod according to the invention will be described in detail byreferring to FIG. 1 to FIG. 13.

[0073] As shown in FIG. 1, the line switching system according to anembodiment comprises terminal devices 101 (101A, 101B), duplex switchingdevices 102 (102A, 102B), transmission devices 103 (103A, 103B, 103C,103D), and networks 104 (104A, 104B) It is built through connecting theterminal device 101A to the duplex switching device 102A, the terminaldevice 101B to the duplex switching device 102B, and also connectingbetween the duplex switching device 102A and the duplex switching device102B via a present system line (present line) used for the presentcommunication and the standby system line (the standby line which isreplaceable with the present line) In between the duplex switchingdevices 102A and 102B, that is, between the present system line and thestandby system line, the transmission devices enabling a long-distancecommunication between the terminal device 101A and the terminal device101B are provided. The transmission devices 103A and 103B are connectedto the present system line and the transmission devices 103C and 103Dare connected to the standby system line, respectively.

[0074] In the embodiment as shown in FIG. 1, the network 104A isconnected between the transmission device 103A and the transmissiondevice 103B, and the network 104B is connected between the transmissiondevice 103C and the transmission device 103D, respectively. The network104A and the network 104B may simply be relay networks and the structurewithin each network is not an issue. Further, it is also possible todirectly connect between the transmission device 103A and thetransmission device 103B, and between the transmission device 103C andthe transmission device 103D without having the networks 104A and 104Bprovided in between.

[0075] The line switching system according to the embodiment uses a lineswitching method (duplex switching method) with the on-signal statebeing the trigger. The system comprises: the terminal device 101A andthe terminal device 101B for transmitting and receiving data; the duplexswitching devices 102 (102A, 102B), which judge the line state of datafrom the terminal device 101A and the terminal device 101B on thetransmission side based on the presence of the reception signal and,when it judges that there is no reception of signal due to a faultgenerated in the line, select the line system with no fault; andtransmission devices 103 (103A, 103B, 103C, 103D) for transmitting thenotification to an opposing station (duplex switching device) via thenetwork 104.

[0076] The duplex switching devices (line switching devices) 102 (102A,102B) comprise fault detection parts 121 (121A, 121B) for detectinggeneration of a fault in the line, line switching parts 122 (122A, 122B)for switching the line to be used, and fault notification parts 123(123A, 123B) for notifying the generation of the fault.

[0077] The fault detection parts 121 detect the generation of faultthrough checking whether or not a recognizable signal is detected fromthe connected line within a prescribed time. The generation of fault,for example, is an incommunicable state caused by cut in the cable.

[0078] The line switching parts 122 switch the present line to thestandby line thereby to achieve the communication between the terminaldevice 101A and the terminal device 101B when the fault detection parts121 detect the generation of fault in the present system line.

[0079] Further, the fault notification parts 123 notify the generationof fault to the other duplex switching device when the fault is detectedin the fault detection parts 121.

[0080] Transmission devices 103 (103A, 103B, 103C, 103D) comprise faultdetection parts 131 (131A, 131B, 131C, 131D) for detecting generation offault and fault notification parts 132 (132A, 132B, 132C, 132D) fornotifying the detected generation of fault.

[0081] The fault detection parts (transmission side fault detectionunit) 131 detect the generation of fault due to the fact that arecognizable signal from the line is not detected within a prescribedtime or receiving notification on the generation of fault.

[0082] Also, the fault notification parts (transmission-side faultnotification unit) 132 notify (transfer the alarm) the generation offault when the fault detection parts 131 detect the fault.

[0083] The above-described networks 104A and 104B are communicationnetworks for transmitting notification using transmission devices.Examples may be SONET/SDH and the like.

[0084] The example of the configuration shown in FIG. 1 shows asimplified configuration in bilateral symmetry with respect to thenetwork as the point of symmetry. In the following, it will be describedby referring to the state where the transmission devices are directlyconnected to each other with the network 104 being omitted.

[0085] As for the transmission devices 103, the ones to be provided onA-side (the present system line side) selected by the duplex switchingdevice 102A and the duplex switching device 102B are to be thetransmission device 103A and the transmission device 103B, and the onesto be provided on B-side (the standby system line side) are to be thetransmission device 103C and the transmission device 103D. The fourtransmission devices are provided in different area but are the samedevices.

[0086] The above-described transmission devices 103 (103A, 103B, 103C,103D), when detecting line fault at the network connecting point, afault in the transmission devices themselves, and a fault at theconnecting points between with the duplex switching device 102A and theduplex switching device 102B, notify the generation of fault throughinterrupting the output of signals to the duplex switching device 102Aand the duplex switching device 102B, thereby triggering the duplexswitching device 102A and the duplex switching device 102B to performjudgment for switching.

[0087] Further, the above-described terminal devices 101, the duplexswitching devices 102, and the transmission devices 103 comprises acommunication part (not shown), respectively, thereby enablingcommunication between the connected devices described above.

[0088] Next, the duplex switching devices 102 (102A, 102B) will bedescribed by referring to FIG. 2. The duplex switching devices 102(102A, 102B) have a function of switching the line from the presentsystem line to the standby system line to be used for the communicationbetween the terminal device 101A and the terminal device 101B.

[0089] The duplex switching devices 102 (102A, 102B) comprise a C-port126 h on the terminal side for connecting the terminal devices, anA-port 126 f on the transmission path side for connecting thetransmission device on the present system line, and a B-port 126 g onthe transmission path side for connecting the standby system line, andachieve duplex system switching through judging the line state of theA-port 126 f and the B-port 126 g on the transmission path side.

[0090] Further, the above-described fault detection parts 121 comprisefault detection circuits (121 f, 121 g, and 121 h) provided for eachport. The above-described line switching parts 122 comprise a switch 150and a switching control circuit 160. The above-described faultnotification parts 123 comprise output control circuits (123 f, 123 g,123 h) provided for each port.

[0091] The input side of the C-port 126 h on the terminal side comprisesan input terminating part 124 h for terminating the signal inputted fromthe C-port 126 h and a fault detection circuit 121 h for detecting thefault from the received data, and is connected to the switch 150 whichselects the transmission path.

[0092] There is a switching control circuit 160 provided for judging theline state of data transmitted from the A-port 126 h on the transmissionpath side and the B-port 126 g on the transmission path side. The switch150 for selecting the line (selection system) used for communicationbetween the terminal device 101A and the terminal device 101B iscontrolled based on the result judged by the switching control circuit160. Data from the selection system (line) is outputted from the C-port126 h. The output side of the C-port 126 h comprises an output controlcircuit 123 h for controlling the output of the C-port throughmonitoring the fault state on the line side and an output terminatingpart 125 h for terminating the output signal.

[0093] The inside structures of the input terminating part 124 h and theoutput terminating part 125 h vary depending on whether the interfacebetween the devices is optical or electrical. However, in any case, itcan judge the fault state by detecting the loss of the signal (the statewhere there is no changing point for a prescribed period or longer) andthe same configuration can be achieved as the block. In other words, bychanging the input terminating part 124 h and the output terminatingpart 125 h, it is possible to achieve an optical communication orelectrical communication between the devices. The same is true for theinput terminating parts 124 and the output terminating parts 125 in theA-port and B-port.

[0094] The input side of the A-port 126 f on the transmission sidecomprises an input terminating part 124 f for terminating the signalinputted from the A-port 126 f and a fault detection circuit 121 h fordetecting the fault from the received data, and is connected to theswitch 150 which selects the transmission path. The output side of theA-port 126 f comprises an output-control circuit 123 f for controllingthe output of the A-port through monitoring the fault state on the lineside and an output terminating part 125 f for terminating the outputsignal.

[0095] Also, the input side of the B-port 126 g on the transmission pathside comprises an input terminating part 124 g for terminating thesignal inputted from the B-port 126 g and a fault detection circuit 121g, and is connected to the switch 150 which selects the transmissionpath. The output side of the B-port 126 g comprises an output controlcircuit 123 g for controlling the output of the B-port throughmonitoring the fault state on the line side and an output terminatingpart 125 g for terminating the output signal.

[0096] The control terminal 127 is connected to a switching controlcircuit 160 of the duplex switching devices 102 (102A, 102B) and is usedfor monitoring the state of the duplex switching devices 102 and foroutputting a forcible switching instruction.

[0097] Now, the outline of the above-described line switching systemaccording to the embodiment will be described.

[0098] The embodiment provides a method of performing an automaticswitching of the lines to the standby line with no fault at a point ofdetecting a fault when the line is duplicated to a present system lineand a standby system line in a system with a line-duplex structure suchas the interface of SONET/SDH having no switching protocol.

[0099] In other words, it is a system comprising a present system lineand a standby system line which can be switched. The system, even whenit is built to achieve communication using a protocol without a functionof switching the lines, can achieve switching of the lines remarkablyfaster than that of the case using a routing protocol, e.g., as fast asthe rate not much slower than that of the case achieved by a protocolwith a function of switching the lines such as SONET/SDH when the faultis detected. As the system for performing communication using a protocolwithout the function of switching the lines, it is applied to a networkusing Ethernet® devices and the like which transmit data using Etherframe and the like.

[0100] The embodiment, as shown in FIG. 1, is applied to the case ofduplex structure in which the duplex switching device 102 is provided inbetween the transmission device 103 and the terminal device 101 andnotification is transmitted by the transmission device 103 viatwo-system lines of a present system line and a standby system line. Inthe embodiment, when a line fault is generated, it does not change theprotocol between the transmission device 103 and the terminal device 101but uses a line switching method using the non-signal state as thetrigger for switching the lines. In the method, an alarm for the linefault is transferred and notification on the generation of line fault istransmitted from the transmission device 103 to the terminal device 101through interruption of the signal (interrupting the output of signal).The state is detected by the duplex switching device 102 providedbetween the transmission device 103 and the terminal device 101 as thetrigger for switching.

[0101] When a line fault is generated, as shown in FIG. 3, FIG. 5 andFIG. 6, from the fault point towards the data transmission direction,notification on the fault state (non-signal state) is always transmittedto the transmission device 103, the duplex switching device 102, and theterminal device 101 on the opposing side so that the duplex switchingdevice 102 can recognize the generation of fault. When the duplexswitching device 102 detects the fault, it transmits the notification onthe fault state (non-signal state) to the down-route line (the linetowards the reverse (the other) direction of the line with a fault outof the full duplex line). The notification is sent out intermittentlythrough alternately transmitting the signal-down state and signal-upstate from the duplex switching device 102 to the transmission device103, to the transmission device 103 on the opposing side, and to theduplex switching device 102 on the opposing side. The duplex switchingdevices 102 on both stations recognize the generation of fault with noinconsistency. In the description of the present invention, the routefrom the fault generating point to the duplex switching device on theopposing side is defined to be an up route and the reverse directionfrom the duplex switching device to the duplex switching device on theopposing station is defined to be a down route.

[0102] It has been described that the signal for notifying thegeneration of fault is to be transmitted to the down-route line. Thelines used for connecting in between each device in the line switchingsystem according to the embodiment are full duplex lines consisting of atransmission line and a reception line. Thus, when a fault is detectedin one of the full duplex lines, the signal is transmitted (notified)using the other line out of the full duplex lines.

[0103] When a fault is generated in a part (section) between theterminal device 101 and the duplex switching device 102 where the lineis not duplicated, as shown in FIG. 7 and FIG. 8, the link of theterminal device on the opposing station is downed through transmitting alink-down pattern to the opposing station of the line selected by theduplex switching device 102. At this time, switching operation is notperformed.

[0104] The alarm transferred from the fault generating point to thedown-route direction is transmitted intermittently as described. Thus,the route of the transferred alarm (notification on the generation offault) becomes a loop shape. However, when the fault is restored, thealarm transfer in the down-route direction is intermittently performedso that the route is interrupted thereby restoring to the normal state.

[0105] When a fault is generated, an alarm notification is transferredto the duplex switching device 102 so that it operates so as to selectthe line with no fault. Therefore, when there is a fault continued to begenerated in one system only (either one of the present system line orthe standby system line), the duplex switching device 102 on theopposing side continues to select the same system. Further, when a faultis generated in both systems (both the present system line and thestandby system line), or when the fault on the port-A side is restored,it has a function of selecting the consistent system by the duplexswitching devices 102 on the opposing stations through always selectingthe port-A side when the faults in both systems are restored.

[0106] As in the Ethernet®, when a link is established by a protocolbetween the transmission device 103 and the terminal device 101, it isnecessary to terminate the protocol at the connecting point. If a MACterminating function for terminating the protocol is provided in theduplex switching device 102, the scale of the hardware becomes large sothat the price of the device itself increases. In order to cope with theproblem, MAC termination is not performed in the duplex switching device102, and uses a system in which the duplex switching device 102 isprovided as if it is a transmission path and judgment for switching isperformed through monitoring the input of the signal and the non-signalstate. Therefore, with the line switching system according to theembodiment, it is possible to achieve the duplex switching device itselfat a low cost.

[0107] Further, the duplex switching device 102 has a function offorcibly switching the line to be used through selecting a switchingsystem device. As the forcible switching system, a method is used inwhich a forcible switching is performed through generating a falseoptical loss state (no output state) for the originally selection system(the line used at present) so that the switching operation starts as inthe case of the actual switching. Thus, in the embodiment, the forcibleswitching function can be achieved without providing another judgingcircuit for switching.

[0108] Also, switching is performed by monitoring the fault state of theline to be switched to, so that it is possible to avoid the cut in theline after the switching caused by a fault in the line to be switchedto.

[0109] Further, the duplex switching device 102, when the power sourceis supplied, continues the interruption of output to the standby lineside (B-port side) longer than that of the present line side (A-portside) at the time of initially booting the device. Thereby, when theinitial booting is completed, it starts to operate by selecting theA-port side as long as there is no fault generated in the present line(the line on the A-port side).

[0110] Therefore, when the power source is supplied, the duplexswitching device 102 selects the same system (the line to be used)between the duplex switching devices of both stations so as to avoid thestate continuing to select the different system (line).

[0111] In recent years, the rate of interface between the devices hasbeen improved along the increase in the capacity of communication.Conventionally, the transmission device is a multiplex device withSONET/SDH and a duplex method used in SONET/SDH has been applied whenduplicating the line. However, a high-speed interface in the standard ofEthernet® has been introduced and it has been more frequently used inthe section of transmission device between the terminal device. In thiscase, it is possible to use the line using Ethernet® through duplicatingit into a present system line and a standby system line. However, theinterface of Ethernet does not have a duplex switching protocol like theconventional SONET/SDH interface so that a method has been employed inwhich the communication route (the line used for communication) is resetin the host routing protocol. With this method, it takes incrediblylonger time from the generation of fault to switching the line to thestandby system line compared to the duplex switching by a protocolhaving a function of switching the line such as SONET/SDH, therebyloosing a large amount of data. The invention is to achieve high-speedduplex switching in the interface of Ethernet® without a function ofswitching the line through using the non-signal state in the sectionbetween the transmission device and the terminal device as the switchingtrigger without changing the protocol.

[0112] As a function required for the transmission device 103, there isa function of interrupting the output of the terminal device side (theline connected to the duplex switching line 102) when there is a faultgenerated. Further, the duplex switching device 102 is provided betweenthe terminal device 101 and the transmission device 103 thereby to leavethe switching processing itself to the duplex switching device.Therefore, the terminal device 101 and the transmission device 103normally operate even when the line is not duplicated (the case withpresent line only) and, in the case of duplicating the line afterwards,it can be achieved by adding a transmission device and a duplexswitching device for the standby system line.

[0113] When fabricating the duplex switching device 102, the hardwarebecomes complicated if switching is achieved by performing thetermination including the protocol. As a result, the price of the duplexswitching device 102 is increased. In order to solve this, switching ofthe line to the standby system line is achieved through simply judgingwhether or not the input signal is interrupted (non-signal state). Theduplex switching device 102 has a configuration comprising a detectioncircuit for detecting the interruption of the input signal (non-signalstate) and a selector switch for system selection thereby achieving thehardware with a simple structure.

[0114] In the embodiment, when detecting a fault generated on thetransmission path is detected, an alarm is transferred to the terminaldevice 101 side for triggering the line switching. If only the triggeris supplied, a fault is generated in a plurality of points. Thus, whenit is restored, the different systems (selected line) may be selectedbetween both duplex switching devices so that self-restoring may not beachieved. During the fault, it is necessary to keep detecting the faultin the duplex switching device on both stations. Therefore, thetransmission device 103 detecting the generation of fault needs totransfer the alarm to the duplex switching device 102 on both stations.

[0115] Transferring of the alarm to the transmission device 103, theduplex switching device 102, and the terminal device 101 at the time ofa fault can be achieved through notifying the state of fault. The duplexswitching device 102 achieves switching of the duplex line by switchingthe system (the line to be used) after detecting the fault. Also, it isnecessary to transfer the alarm to the duplex switching device on theopposing station thereby to give a switching trigger to the notifiedduplex switching device. In other words, the fault detected by eitherone of the duplex switching device needs to be alarm-transferred to theopposing duplex switching device.

[0116] It is not possible to recognize the whereabouts the fault isgenerated when the alarm is being transferred. Thus, the duplexswitching device on the opposing station transfers the alarm to theopposing device when detecting a fault. In this alarm-transfer method,the alarm transfer is performed from the fault generating point as thestarting point and loops between with the opposing duplex switchingdevice thereby to be transferred to the fault generating point. If thefault detected by the duplex switching device is transferred as it istowards the opposing duplex switching device, the alarm transfer iscontinued without a break of the fault even at the point where the faultis restored. Thus, it cannot break the endless loop of the alarm. Inorder to solve this, when transferring the alarm for the fault detectedby the duplex switching device to the opposing duplex switching device,interruption of signal (non-signal state) and the link down pattern aretransmitted periodically thereby to intermittently transfer the alarm.Thereby, it prevents the endless loop of the alarm transfer when thefault is restored.

[0117] Further, in the line switching system according to theembodiment, when there is a fault generated in both duplex lines andbecomes incapable of communication, the duplex switching devices on bothstations are to select the system on the A-port side. Therefore, it canbe operated in such a manner that both stations always select the samesystem when it is restored from the fault.

[0118] If there is no such function for selecting the A-port side whenit is incapable of communication, there may be cases where both stationsselect different systems depending on the timing by which double faultsare generated. When the faults are restored from that statesimultaneously, the devices continue to operate while keep selecting thedifferent systems, so that it becomes impossible to break from thestate. In order to solve the problem, the duplex switching device 102according to the embodiment operates to select the A-port at the time ofdouble faults. Also, it is booted through generating a false fault forthe B-port so that the A-port is to be selected when the power source issupplied to the device. Thus, the devices can be started to operate byselecting the same active system (the lines to be used).

[0119] Next, operation of the line switching system according to theembodiment will be described.

[0120] First, the basic operation will be described by referring toFIG. 1. Data from the terminal device 101A is transmitted to the duplexswitching device 102A. The duplex switching device 102A always monitorsthe state of signals transmitted from the A-port and B-port connected tothe transmission path at all times. When there is no fault generated inthe system (line), which is selected at present, the duplex switchingdevice 102A continues to select the present system and switches the linewhen there is a fault generated in the system selected at present.

[0121] The generation of fault is detected through judging whether ornot the data inputted to the A-port and B-port of the duplex switchingdevice 102A is interrupted. In other words, the fault detection part121A judges it as a generation of fault when a recognizable signal fromthe line is not detected for a prescribed time. The prescribed time maybe longer than the maximum value of the continued state of time wherethe signal is interrupted by a protocol. Also, it may be the timeobtained by adding time for confirming the error to the maximum value.

[0122] The line is switched when it is judged that the fault iscontinued even after the switching protection time has passed. In theduplex switching device 102A, when there is a fault generated in theinput of either the A-port or the B-port connected to the transmissionpath, the generation of fault is also notified to the opposing connecteddevice. The alarm is transferred to the duplex switching device 102B onthe opposing station side via the transmission device 103A and thetransmission device 103B, or via the transmission device 103C and thetransmission device 103D.

[0123] The alarm transfer by the transmission device 103 and the likewill be described by referring to the case where there is a faultgenerated in the line 105 c shown in FIG. 3. When there is a faultgenerated in between (line 105 c) the transmission device 103A and theduplex switching device 102A, first, the transmission device 103 detectsit as a reception fault. The transfer data at each point shown in FIG.3, at the time of detecting the loss of input as the reception fault, isshown in FIG. 9 as a transmission data at the time of transferring thealarm.

[0124] There is no fault generated in between (line 105 g) thetransmission device 103A and the transmission device 103B so that anormal transmission is possible. At this time, the reception faultdetected by the transmission device 103A is notified to the transmissiondevice 103B on the opposing side through generating a packet fornotifying the fault (reception fault notification packet). Uponreceiving the reception fault notifying packet, the transmission device103B notifies the generation of the fault to the duplex switching device102B through interrupting the output to the line 105 m. The switchingdevice 102B notifies the non input to the terminal device 101B throughthe line 105 r while notifying the output side 105 n of the A-portthrough periodically interrupting the output and transmitting the linkpattern. In other words, the fault detection part 123B notifies thedetected fault through periodically repeating the interruption of theoutput signal and transmitting the link down pattern for downing thelink in the protocol.

[0125] The fault is not notified through continuously interrupting theoutput because of the following reason. The link down pattern will bealso described in the followings. As shown in FIG. 3, the alarm at thetime of fault is transferred (generated fault notification) turning backand forth in between the duplex switching device 102A and the duplexswitching device 102B. Thus, the route transferring the alarm is to bein a loop. If the alarm is always being transferred in between thedevices, the transferred fault generation notification becomes a factorfor regenerating a fault after the fault is being restored. Therefore,it cannot break from the loop state.

[0126] Therefore, the generation of fault is continuously transferredfrom the fault generating point until reaching the duplex switchingdevice 102B and the interruption of the output and the link down patternare periodically transmitted in the route from the duplex switchingdevice 102B to the opposing duplex switching device 102A thereby toprovide a non-signal state and a signal state alternately. Thereby, itavoids the alarm to be continuously transferred in the loop state.

[0127] At this time, the no-output state is to be defined sufficientlylong for the alarm transfer delay time between with the opposingstations. The relation between the transfer delay time, time for theoutput interruption, and the link down pattern transmission time will bedescribed by referring to FIG. 4.

[0128]FIG. 4(a) shows the case where the above-described time for theoutput interruption is shorter than the transfer delay time. FIG. 4(a-2)shows the state in which the signal is delayed for the transmissiondelay time with respect to the case shown in FIG. 4(a-1). Further, FIG.4B shows the case where the above-described time for the outputinterruption is sufficiently longer than the transmission delay time.FIG. 4(b-2) shows the state in which the signal is delayed for thetransmission delay time with respect to the case shown in FIG. 4(b-1).In the figures, “H” level denotes the non-output state due to thegeneration of fault and “L” level denotes the link down patterntransmission time.

[0129] When notification on the generation of fault is transmitted in aloop state due to a fault generated at a fault generating point, if, asshown in FIG. 4(a), the time for output interruption is shorter than thetransfer delay time at the point where the notification is transferredto the point just before the fault generating point, the duplexswitching device 102 waits judgement based on the received signal duringthe transfer delay time in order to avoid a misjudgment. As a result,the non-signal state shown in FIG. 4(a-1) is not used for the judgmentso that the duplex switching device 102 misunderstands that the fault istemporarily restored. In other words, there may be cases where theduplex switching devices on both stations recognize the fault as thedifferent fault state.

[0130] On the contrary, by setting the time for the output interruptionsufficiently longer than the transmission delay time as shown in FIG.4(b), it can avoid the affect caused by waiting the judgment describedabove for the transmission delay time and able to recognize the outputinterruption. Further, even if there is a difference in the recognizedtime because of the transfer delay time in both duplex switchingdevices, there is a time zone in which both of the duplex switchingdevices can commonly recognize the fault state. Therefore, it ispossible to avoid such a problem of repeatedly recognizing the faulteven after the fault is temporarily restored.

[0131] In the periodical transmission of the output interruption and thelink down pattern, the time for transmitting the link down pattern perperiod is set to be longer than the time for the output interruption.Thereby, it is possible to avoid the endless loop state where thedevice, which transferred the alarm by detecting the fault, detects thefault by the alarm transferred from the device itself.

[0132] The minimum requirement for avoiding the endless loop state is toset the time for transmitting the link down pattern longer than that ofthe output interruption per period of the alarm transfer. It has beenverified by inventor of the present invention that it is preferable thatthe time for transmitting the link down pattern be about four timeslonger than that of the output interruption per period. For example,provided that the maximum data transfer delay time between the terminaldevice 101A and the terminal device 101B is 10 ms, if the time for theoutput interruption in one period is 100 ms, and the transmission timeof the link down data is 400 ms and the one period is 500 ms, there isno such problem to be generated as the endless loop state as describedabove, since there is a four-time interval to be present in between.Further, the time for the output interruption is sufficiently longerthan the transfer delay time so that no such problem in regards to thetransfer delay is generated. Therefore, it is confirmed that the devicesnormally operate.

[0133] Now, the link down pattern will be described. When transmissionis achieved in between the terminal device 101A, the transfer device103A and the transmission device 103C, as well as in between theterminal device 101B, the transmission device 103B and the transmissiondevice 103C using Ethernet frame, link up control is performed inbetween the devices and it becomes possible to transfer data at thepoint when the link is established. When there is a generation of fault,communication cannot be normally performed and the link is down. Duringthe fault, the link down pattern is sent out to keep the link-downstate. As the link down pattern, a pattern in violation of 8B10B codeused for transmitting Ether frame may be generated. For example, ON/OFFsignal with the time length different from the 8B10B code may begenerated.

[0134] In the repeated signal of the output interruption and the linkdown pattern inputted to the transmission device 103B, the outputinterruption transmitted from the transmission device 103B to thetransmission path 105 h is converted to a reception fault notificationpacket to be transmitted to the opposing transmission device 103A. Whenthe link down pattern is detected by the transmission device 103B, thetransmission device 103B performs a link down control for downing thelink between the terminal device 101B and transfers it as a link downnotification packet to the opposing transmission device 103A. Thetransmission device 103 receiving the data interrupts the output whilereceiving the reception fault packet and, when receiving the link downnotification packet, performs link down control for the terminal device101A to be in the link down state. When the duplex switching device 102Areceives these data, it returns the data to the transmission path sideand transmits the same pattern to the A-port (line 105 c).

[0135] The fault notification is sent to the fault generating point. Theoutput to the C-port of the duplex switching device 102A is continuouslyinterrupted thereby to notify that the line side cannot be used. Theduplex switching device 102A and the duplex switching device 102B, whendetecting a switching trigger (non-signal state) in the A-port, wait fora switching protection time. During this time, if the continuousinterruption is detected, the devices move onto the switchingprocessing. When there is no fault generated in the B-port to beswitched to, the active system is switched to the B-port. When there isalso a fault generated in the B-port to be switched to, the switchingdevices do not perform switching processing and keep selecting theA-port. Further, when there is a fault generated in both the A-port andB-port under the state where the B-port is selected, the switchingdevices select the A-port thereby to avoid the state in which bothstations select the different systems when the fault is restored. Theunselection system, in the duplex switching device 102A and the duplexswitching device 102B, returns the input on the transmission path side(A-port or B-port) to the output on the transmission side so that thetransmission device on the side connected to the terminal device becomesa return connection. The transmission device performs link up controlfor the device itself so as to establish the link. The transmissiondevice in which the standby system is selected operates by performinglink up for the device itself as long as there is no fault generated inthe transmission path. The standby system waits in such a state so thatit is possible to execute the switching after confirming whether or notthe standby system line is normal between the duplex switching device102A and the duplex switching device 102B before switching the activesystem.

[0136] The operation of the system has been described heretofore byreferring to FIG. 3. Next, the switching operation of the duplexswitching device 102A and the duplex switching device 102B will bedescribed in detail by referring to FIG. 2.

[0137] When the duplex switching device 102 detects a fault in theA-port 126 f, data inputted via the input terminating part 124 f isjudged in the fault detection circuit if there is a non-signal state.The judgment is performed through monitoring the state of the faultdetection circuit 121 f in the switching control circuit 160 inside theduplex switching devices 102 (102A, 102B). If the signal is interrupted,the switching control circuit 160 outputs an instruction to the outputcontrol circuit 123 f to interrupt the output periodically and, at thesame time, outputs the link down pattern generated inside the outputcontrol circuit 123 f. At the same time, the switching control circuit160 outputs an instruction to the output control circuit 132 h of theC-port to interrupt the output.

[0138] After detecting the fault in the switching control circuit 160,the fault state is monitored until a certain switching protection timehas passed. When the fault is continued even after the switchingprotection time has passed, the switching control circuit 160 outputs aninstruction to the switch 150 thereby to switch to select the B-port.When the fault is discontinued after the switching protection time,switching is not executed.

[0139] Before the switching is executed, the output of the faultdetection circuit 121 g of the B-port is connected to the input of theoutput control circuit 123 g thereby forming a loop back state. When theswitching is executed, the fault detection circuit 121 f of the A-portconnected to the output control circuit 123 h of the C-port and thefault detection circuit 121 h of the C-port connected to the outputcontrol circuit 123 f of the A-port are changed to be in such a form inwhich the fault detection circuit 121 g of the B-port is connected tothe output control circuit 123 h of the C-port and the fault detectioncircuit 121 h of the C-port is connected to the output control circuit123 g of the B-port.

[0140] On the other hand, on the A-port side, the output of the faultdetection circuit 121 f and the input of the output control circuit 123f are to be connected. When the B-port is in a normal state, there is nofault detected in the fault detection circuit 121 g of the active system(B-port) so that the interruption of the output to the output controlcircuit 123 h of the C-port is canceled. The switching control circuit160 notifies the fault state and the selection system to the controlterminal 127 connected thereto.

[0141] Further, if a forcible switching of the system is desired duringthe operation, the control terminal 127 outputs a switching instruction.For example, when forcibly switching the port to the A-port while theB-port is in operation, it operates as follows. A user inputs anddesignates the system to be forcibly switched to from the controlterminal 127. At this time, it will be described by referring to a casewhere the user designates the A-port.

[0142] The switching control circuit 160, upon receiving the instructionfrom the control terminal 127, starts a processing so that the B-portinterrupts the signal output. The processing is performed throughoutputting the instruction for interrupting the output to the outputcontrol circuit 123 g of the B-port from the switching control circuit160. By keeping the output interruption to the connected transmissiondevice 103 for a certain time (for example, one second), the connectedtransmission device 103 judges that there is a generation of fault andperforms the alarm transfer. The operation of the alarm transfer isperformed by the same processing as that of the case where there is anactual fault generated on the line. The fault is detected on the B-portside by the opposing duplex switching device so that the switching isexecuted to the A-port side. At this time, the opposing duplex switchingdevice also transfers the alarm to the duplex switching device sidewhich generated a false fault. In the duplex switching device sidereceiving the alarm, the fault is also detected on the B-port side sothat the switching processing to the A-port side is executed.

[0143] As described, when forcibly switching the system, it can beachieved through generating a false fault by outputting the instructionfor interrupting the output to the output control circuit to be switchedfrom. Therefore, it is not necessary to provide an additional circuit.

[0144] At the time of the switching, if there is a fault generated inthe port to be switched to, the processing itself for interrupting thesignal output is not performed. Thereby, it is possible to avoid thestate to be incommunicable after completing the switching operation, andthe present communication state can be maintained. The fault state canbe monitored in the control terminal 127 so that whereabouts the faultis generated can be detected in the control terminal 127.

[0145] When the power source is supplied to the duplex switching device102, a processing of matching the selection system is performed throughutilizing the processing of interrupting the output signal. The powersource is supplied to each device so that the line switching systemsaccording to the embodiment on both station are to be in operation.However, in general, each device is placed in different positions sothat the order of supplying the power source to the devices cannot bedefined.

[0146] In the invention, it provides with such a system that bothstations start to operate by selecting the same system in such a case.The duplex switching device 102, after the power source is supplied,performs the setting within the device so as to be in the state foroperation. At this time, if it is operated by interrupting the signaloutput to the standby side (B-port side) and keeps the signal outputonly to the present side (A-port) for a prescribed time (for example,one second) even after the device itself can be in an operable state, itselects the present side (A-port) to be in operation when there is nofault in the present-side line (A-port). In this circuit, it only needsto control the interruption of the output signal to the standby side(B-port side) for a long time so that it can be achieved using theoutput control circuit 123 g of the B-port shown in FIG. 2, which isused in the normal switching operation. The switching control circuit160 manages the control of interrupting the signal output interruptionthrough monitoring the supply to the power source.

[0147] Further, the case of a fault generated in the line 105 g shown inFIG. 5 shows the alarm transfer when there is a fault generated in thetransmission path (the line 105 g) between the transmission device 103Aand the transmission device 103B. At this time, the alarm transfer dataat each point is shown as transmission data (a fault between thetransmission device 103A and the transmission device 103B) at the timeof alarm transfer in FIG. 10. In the case of a fault generated in theline 105 g shown in FIG. 5, the same operation as the case describedabove by referring to FIG. 3 is performed in regards to the alarmtransfer except that the generating point is different. The alarm istransferred to the section from the duplex switching device 102A to theoutput point 105 g of the transmission device 103A shown in FIG. 5through periodically outputting the output interruption and the linkdown pattern.

[0148] Also, the case of a fault generated in the line 105 m shown inFIG. 6 shows the alarm transfer when there is a fault generated inbetween the transmission device 103B and the duplex switching device102B. At this time, the alarm transfer data at each point is shown astransmission data (a fault between the transmission device 103B and theduplex switching device 102B) at the time of alarm transfer in FIG. 11.In the case of a fault generated in the line 105 m shown in FIG. 6, thesame operation as the case described above by referring to FIG. 3 isperformed in regards to the alarm transfer except that the generatingpoint is different. The alarm is transferred to the section from theduplex switching device 102A to the output point 105 m of thetransmission device 103B shown in FIG. 6 through periodically outputtingthe output interruption and the link down pattern.

[0149] The case of a fault generated in the line 105 m shown in FIG. 6shows the case where there is a fault generated in the non-duplexsection between the terminal device 101A and the duplex switching device102A. In this case, the link down pattern is generated in the duplexswitching device 102A thereby to down the link of the terminal device101B on the opposing side so as to inform that the line is notavailable.

[0150] In other words, the notification shown by double chain lines inFIG. 7 represents the notification route under the link down state. Theduplex switching device 102A can detect the fault by the inputinterruption. Thus, when detecting the fault, it outputs the link downpattern to the line 105 c. The transmission device 103A, upon receivingthe link down pattern, performs the link down control thereby to downthe link between with the terminal device 101A. The transmission device103A, when the link is down, transfers the link down notification packetto the transmission device 103B on the opposing station in order tonotify the link down state. The transmission device 103B, upon receivingthe link down notification packet, downs the link between the terminaldevice 101B and notifies the link down state to the transmission device103A on the opposing side via the line 105 h. At this time, the linkbetween the transmission device 103A has been already down so that thedevice maintains the link down state.

[0151] In this state, the line switching is not performed since thefault cannot be restored to be communicable even though the line isswitched to the other system (the other line).

[0152] The case of a fault generated in the line 105 b shown in FIG. 8shows the case where there is a fault generated in the non-duplexsection between the terminal device 101A and the duplex switching device102A as in the case shown in FIG. 7. At this time, in the method inwhich the terminal device 101A interrupts the output thereby to down thelink, as in the case shown in FIG. 7, the link down patter is generatedin the duplex switching device 102A thereby to down the link of theterminal device 101B on the opposing side so as to inform that the lineis not available.

[0153] In other words, the notification shown by double chain lines inFIG. 8 represents the notification route under the link downstate. Whenthe terminal device 101A downs the link between with the transmissiondevice 103A through performing the link down control, the input signalof the duplex switching device is not interrupted. Thus, it cannot judgethe generation of fault so that the link down pattern cannot betransmitted. The terminal device 101A performs the link down controlbetween with the transmission device 103A so that the link is to bedown, thereby achieving the same state as that of the case where theterminal device 101A interrupts the output. Further, transfer of thelink down state from the transmission device 103A to the transmissiondevice 103B is performed by the same method as that shown in FIG. 7.

[0154] In this state, the line switching is not performed since thefault cannot be restored to be communicable even though the line isswitched to the other system. At the time of a fault being generated onthe input side of the terminal device 101A, when the terminal device101A interrupts the output, the operation of the system is the same asthat of the case shown in FIG. 7 except that the fault generating pointis different from the case shown in FIG. 7. At the time of fault in thisexample, two types of operations are possible depending on the operationof the terminal device 101A.

[0155] As described, with the line switching system according to theembodiment, at the time of switching the duplex lines in the duplex-linestructure, the generation of fault in the transmission path is notifiedto the duplex switching device by interrupting the signal thereby totrigger the switching of the line. Therefore, it is applicable to asystem with no switching protocol. For example, it can be applied toEthernet® devices which perform transfer using the Ethernet frame.

[0156] The line switching method of the embodiment using the non-signalstate as a trigger for switching can be achieved through simply adding aduplex switching device, which performs the duplex switching of theline, in between the terminal device and the transmission device, aslong as the transmission device provided in the transmission path has afunction of transferring the fault state to the opposing transmissiondevice when a fault is generated and a function of interrupting thesignal output to the terminal side. At this time, in the duplexswitching device, switching can be performed upon detecting thenon-signal state as a switching trigger without terminating the protocolin the interface between the terminal device and the transmissiondevice. Therefore, the duplex switching device itself can be achieved ata relatively low cost.

[0157] In the present invention, the fault is continuously transmittedas it is in the state of generation of fault from the fault generatingpoint to the duplex switching device in the data transmission direction.However, when the duplex switching device transmits the generation offault to the opposing duplex switching device upon detecting the fault,it is transmitted periodically. Therefore, even the alarm transfer formsa loop shape with the fault generating point as the starting point, itcan avoid an endless loop in which the alarm is still transferred evenafter the fault is restored.

[0158] Also, the duplex switching device has a function of selecting theA-port side at all times when there is a fault generated in both of theduplex lines. Thus, when restoring from the double faults, arbitraryselection of the system by both stations can be avoided therebypreventing the inconsistent system selection.

[0159] If there is no such function, the duplex switching devices onboth stations select the different systems when there are faultsgenerated in both of the duplex lines. Therefore, when the faults arerestored simultaneously, the devices maintained to be in the state tokeep selecting the different systems. In the present invention, theduplex switching device is to operate so as to select the A-port side atall times in the case where faults are generated in both of the linesand the case where the fault in the A-port side is restored. Thereby, atthe time of the faults in both lines, the duplex switching devices inboth stations are to select the A-port side, thereby avoiding theinconsistent selection of the systems when the fault is restoredsimultaneously.

[0160] Also, at the time of supplying the power source to the duplexswitching device, interruption of the output is continued to the standbyline side (B-port side) of the duplex switching device for a longer timethan to the present line side (A-port side) thereby to complete theinitial booting of the device. Therefore, as long as there is no faultgenerated in the present line side (A-port side), the device starts theoperation by selecting the present line side (A-port side). Thereby, itis possible to avoid the state where the duplex switching devices inboth stations select the different systems when the power source issupplied thereby to prevent the state where the devices cannot breakaway from the state.

[0161] When a forcible switching to the designated selection system isdesired while in operation, it is achieved through interrupting theoutput by the output control circuit of the duplex switching device onthe side to which the line is switched (B-port side if the designatedport is A-port, and A-port if the designated port is B-port). In thiscase, the output control circuit of the duplex switching device can usethe circuit for the regular switching operation. Therefore, it can beachieved by simply adding the control from the switching control circuitwhich has received the control signal from the control terminal. Thus,the forcible switching can be achieved by adding a relativelysmall-scaled circuit without providing hardware exclusively for forcibleswitching.

[0162] Also, when performing a forcible switching, it is executed onlywhen there is no fault generated after checking the state of the line tobe switched to. Thus, it can avoid to be in the incommunicable state dueto the forcible switching.

[0163] Further, there may be cases where, when building the network, atransmission system with no standby line is initially build and thenetwork is expanded through adding the standby system lines when thereliability is required. It can be also achieved in this case throughinserting the switching device between the transmission device and theterminal and additional devices can be flexibly provided.

[0164] As described, in the conventional case, when the non-signal stateis simply transferred as the alarm, the selection of the system selectedby both stations are to be inconsistent depending on the state of thedevices. In this state, if there becomes a state with no fault on theline, the devices cannot break away from the inconsistent. Whenperforming the alarm transfer in the full duplex communication system,the device, upon detecting the reception fault, notifies the fault tothe opposing station through the transmission side line. In this method,notification of the fault starts from the fault generating point,returns between the communication routs on both sides and continuesuntil reaching the fault generating point. In other words, the alarm istransferred in a loop state with the fault generating point as thestarting point. If the alarm transfer is continued at all times, thedevices cannot break away from the loop state of the alarm transfer whenthe fault is restored. Therefore, it faces a problem that the faultcannot be restored.

[0165] The line switching system according to the embodiment does notface such problems even used in a system in which communication isperformed using a protocol without the function of switching the line.Therefore, a highly reliable line switching can be achieved by a fastand reliable operation.

[0166] Next, a line switching system according to another embodiment ofthe present invention will be described by referring to FIG. 12 and FIG.13.

[0167] In this embodiment, a plurality of pairs of terminal devices forperforming communication are provided, unlike the above-describedembodiment having a pair of the devices.

[0168] The line switching system according to the present embodiment, asshown in FIG. 12, comprises: terminal devices 101 (101A, 101B, 101C,101D), duplex switching devices 102 (102A, 102B, 102C, and 102D) andtransmission devices 103 (103A, 103B, 103C˜103H). One of the terminaldevices 101 is connected to the duplex switching devices 102,respectively, and the duplex switching devices 102 are connected toother duplex switching devices via the present system line and thestandby system line to which one of the transmission devices 103 isprovided, respectively.

[0169] Each of the terminal devices 101 (101A, 101B, 101C, 101D) shownin FIG. 12 may be the same as the terminal device 101A and the terminaldevice 101B of the above-described embodiment shown in FIG. 1. Also,each of the duplex switching devices 102 (102A, 102B, 102C, 102D) shownin FIG. 12 may be the same as the duplex switching device 102A and theduplex switching device 102B of the above-described embodiment shown inFIG. 1. Further, each of the transmission devices 103 (103A, 103B,103C˜103H) shown in FIG. 12 may be the same as the transmission device103A, the transmission device 103B, the transmission device 103C and thetransmission device 103D of the above-described embodiment shown in FIG.1.

[0170] Further, each of the duplex switching devices 102 (102A, 102B,102C, 102D) shown in FIG. 12 has a configuration as described byreferring to FIG. 2 and the control of the connection to each port ismanaged by the switching control circuit 160.

[0171] By changing the connecting condition and fixedly connecting theA-port and the B-port, it becomes possible to achieve the network with astructure connected in such a manner as shown in FIG. 13. FIG. 13(a)shows the state where the terminal device 101A and the terminal device101B are connected to be capable of communication, and FIG. 13(b) showsthe state where the terminal device 101C and the terminal device 101Dare connected to be capable of communication.

[0172] When achieving the connection shown as in FIG. 13(a), in thecondition between the duplex switching device 102C and the duplexswitching device 102D are connected to the terminal device 101C and theterminal device 101D via the A-port and the B-port and the systemswitching operation is not performed. In this structure, it is possibleto build a network with a structure in which the lines are duplicatedbetween the terminal device 101A and the terminal device 101B. Theoperation in this case is the same as that of the above-describedembodiment shown in FIG. 1.

[0173] Also, when achieving the connection shown as in FIG. 13(b), theduplex switching device 102A and the duplex switching device 102B areconnected to the terminal device 101A and the terminal device 101B viathe A-port and the B-port and the system switching operation is notperformed. In this structure, it is possible to build a network with astructure in which the lines are duplicated between the terminal device101C and the terminal device 101D. The operation in this case is alsothe same as that of the above-described embodiment shown in FIG. 1.

[0174] In the same manner, in the case where, the duplex switchingdevice 102A and the duplex switching device 102D are connected to theterminal device 101A and the terminal device 101D via the A-port and theB-port, it is possible to build a network in which the line isduplicated between the terminal device 101B and the terminal device101C. In the case where, the duplex switching device 102A and the duplexswitching device 102C are connected to the terminal device 101A and theterminal device 101C via the A-port and the B-port are connected, it ispossible to build a network in which the line is duplicated between theterminal device 101B and the terminal device 101D.

[0175] As described, it is possible to achieve a various networkstructure and duplicate the line through changing the connectingcondition of the duplex switching devices 102.

[0176] Further, if the partner device (terminal device) to whichtransfer is performed changes as the time passes, the condition of theduplex switching device, in the structure according to the embodiment,can be changed as the time passes. In other words, a network can bebuilt, which operates as scheduled by preparing an assigned schedule sothat the network is to be built to perform communication between aterminal device and a prescribed another terminal device via the duplexlines at a prescribed time.

[0177] As described, with the line switching system according to thepresent embodiment, a system can be built in which one of the terminaldevices is connected to the prescribed another terminal device via thelines duplicated to the present system line and the standby system lineby the duplex switching device.

[0178] Each of the embodiments described above is a preferred embodimentof the present invention and various modifications are possible withinthe spirit and the broad scope of the appended claims of the invention.For example, the present system line and the standby system lineaccording to each of the embodiments described above may not need to befixedly decided but any of the line may be decided to be the standbysystem line.

[0179] Further, each of the embodiments described above has beendescribed by referring to the case where one terminal device isconnected to the duplex switching device. However, it is not limited tothis but a plurality of the terminal devices may be connected. In thecase with a plurality of the terminal devices, the line selected(switched) by the duplex switching device according to each embodimentdescribed above is to be shared by a plurality of the terminal devices.Also, the transmission device capable of achieving a long-distancecommunication by the terminal device is to have a transmission capacitycorresponding to the connected terminal devices (the number of lines tobe corresponded).

[0180] Further, in each of the embodiments described above, thetransmission devices are used. However, it is not required for ashort-distance communication, and the duplex switching device andanother duplex switching device may be directly connected via thepresent system line and the standby system line.

[0181] As described, the invention is a line switching system comprisinga present line and a standby line formed to perform communication usinga protocol without a function of switching the line. The line switchingdevice comprises: the fault detection unit for detecting the generationof fault through checking whether or not a recognizable signal isdetected from the line within a prescribed time; and the line switchingunit for switching the line from the present line to the standby linewhich can be replaced with the present line so as to perform thecommunication between the terminal device and prescribed anotherterminal device therethrough, when the fault detection unit detects thegeneration of fault in the present line.

[0182] Thereby, in the system, communication is performed using aprotocol without a function of switching the line. Thus, it is possibleto promptly switch the line to the standby line when the recognizablesignal is not detected from the present line within a prescribed time.Therefore, when there is a fault generated in the present line, a promptline switching can be achieved without changing the basic protocol ofthe network with no requirement for adding an expensive hardware.

[0183] Also, the line switching unit switches the line after theswitching protection time has passed from the time when the generationof fault is detected by the fault detection unit.

[0184] Thereby, it is possible to improve the reliability in the lineswitching when detecting the generation of fault.

[0185] Further, by the line switching method of the present invention,it is possible to achieve the same effect as that of the line switchingsystem of the present invention described above.

[0186] In the above-described embodiments, the line switching system inmultiplex communication and the method have been described. Next, aspecific example of an optical transmission switching device used inmultiplex communication will be described. The optical transmissionswitching device according to the present invention is a switchingdevice for switching the transmission path to be used when there is afault generated in any given transmission path in an opticaltransmission system comprising a plurality of transmission paths.

[0187] In order to define the distinctive feature of the opticaltransmission switching device according to the present invention, itwill be described by making a comparison to a conventional case.Recently, an optical transmission system capable of transmitting a largeamount of data at a high-speed has been widely used. The opticaltransmission system, as shown in FIG. 35, comprises a transmission-sideterminal 210, a transmission-side transmission device 212, atransmission path 213, a reception-side transmission device 214 and areception-side terminal 219.

[0188] The transmission-side terminal 210 has a function of generatingdata and transmitting the data. The transmission-side transmissiondevice 212 is a transmission-side device for transmitting the data fromthe terminal 210 via the transmission path 213. The reception-sidetransmission device 214 processes data received from the transmissionpath 213. The reception-side terminal 219 receives the data from thetransmission device 214.

[0189] With such optical transmission system, the data from the terminal210 can be transmitted to the terminal 219. However, in the opticaltransmission system described above, data transmitted from the terminal210 cannot reach the terminal 219 when there is a fault generated in anysection between with the transmission device 212, the transmission path213, and the transmission device 214. In order to avoid this, an opticaltransmission system has been proposed, which employs a duplex structure.In the system, a present system line and a standby system line areprovided beforehand so that, when there is a fault generated in thepresent system line, the active system is switched to the standby systemline thereby to avoid the communication difficulty.

[0190] The optical transmission system with the duplex structure, asshown in FIG. 36, comprises a transmission-side switching device 211,transmission-side transmission devices 212, 215, transmission paths 213,216, reception-side transmission devices 214, 217, a reception-sideswitching device 218, and a reception-side terminal 219.

[0191] In the optical transmission system with the duplex structure, twolines made of a line consisting of the transmission device 212, thetransmission path 213, and the transmission device 214, and a lineconsisting of the transmission device 215, the transmission path 216 andthe transmission device 217 are provided beforehand. Thereby, throughswitching the two lines by the switching device 211, it becomes possibleto avoid communication difficulty even if there is a fault generated ineither line.

[0192] The transmission device 215, the transmission path 216, and thetransmission device 217 have the same structure and function as that ofthe transmission device 212, the transmission path 213, and thetransmission device 214, respectively.

[0193] The switching device 211 branches data from the transmission-sideterminal 210 into two and transmits the branched data to thetransmission devices 212 and 215, respectively. The switching device 218selects either the transmission device 214 or the transmission device217 as the active system line. When the data from the selected linebecomes invalid, the switching device 218 switches the active system tothe other switching device and selects data from this transmissiondevice and transmits it to the terminal 219.

[0194] Next, outline of the switching operation in the opticaltransmission system shown in FIG. 36 will be described by referring tothe figure.

[0195] Data transmitted from the transmission-side terminal 210 isbranched into two via the transmission-side switching device 211 and thesame data are transmitted to both the present system line and thestandby system line. The transmission device 212 transmits the data tothe transmission device 214 via the transmission path 213 and thetransmission device 215 transmits the data to the transmission device217 via the transmission path 216. When there is a line fault generatedin between the terminal 210 and the transmission device 212 or inbetween the terminal 210 and the transmission device 215, thetransmission device 212 or the transmission device 215 transmitsnotification of the generated fault to the opposing device, thetransmission device 214 or the transmission device 217 so as to notifythat the line is not available. The transmission device 214 or thetransmission device 217, upon receiving the notification, recognizes thegenerated fault and interrupts the output to the switching device 218.

[0196] The switching device 218, when judging that the input signal isinterrupted, continues the data transmission through switching theactive system to the side in which the signal is not interrupted. Theswitching device 218 does not perform switching unless the input of thepresent active system is interrupted. It is a role of the switchingdevice 218 to transmit the data from the system selected as described tothe reception-side terminal 219. The transmission path fault generatedin the transmission device 212, in between the transmission device 215and the transmission device 214, or the transmission device 217 isjudged within the transmission device 214 or the transmission device217. Then, the device notifies the fault to the switching device 218 byinterrupting the output to the switching device 218 thereby to executethe switching.

[0197] In the optical transmission system as described, the outputinterface of the terminal 210 and the input interfaces of thetransmission devices 212 and 215 are to coincide with each other to beconnected, and the output interfaces of the transmission devices 214 and217 and the input interface of the terminal device 219 are to becoincide with each other thereby to be connected. When the interfacesare determined, the interface of the switching device 211 and theterminal 219 to be provided in between the transmission devices 212,215, and the interface of the switching device 218 provided in betweenthe transmission devices 214, 217 are to be determined inevitably. Thatis, the interfaces of the switching devices 211 and 218 are determineddepending on the interfaces of the transmission devices 212, 215, 214and 217 to be used.

[0198] In recent years, there have been a various kinds of interfacesused as interfaces of devices, such as SDH (Synchronous DigitalHierarchy)/SONET (Synchronous Optical Network) interface, various kindsof Ethernet interfaces and the like. Thus, when the duplex structure asshown in FIG. 36 is used, it is necessary to provide a switching devicedepending on an interface whenever the device interface used therein isdifferent.

[0199] For example, SDH/SONET OC48 interface is not compatible with theGigabit Ethernet interface. Thus, it is necessary to develop and providea switching device for the SDH/SONET OC48 interface when using theSDH/SONET OC48 interface, and necessary to develop a switching devicefor the Gigabit Ethernet interface when using the Gigabit Ethernetinterface. Therefore, when the number of the types of interfaces used inthe devices is increased, it becomes necessary to develop switchingdevices corresponding to the interfaces of various types, which istime-consuming.

[0200] It has been described by referring to the case of duplexstructure with two lines in order to simplify the description. However,there faces the same problems in optical transmission system having amultiple structure with three or more lines.

[0201] Further, in an optical transmission system comprising a pluralityof terminals and a plurality of transmission paths, in which eachterminal selects a different transmission path, a cross-connectingdevice is used as a switching device for switching the connectionbetween a plurality of lines. In such optical transmission system, it isnecessary to design a corresponding cross-connecting device when theinterfaces of the terminal and the transmission device vary.

[0202] An object of the present invention is to provide a switchingdevice which can be used without being affected by the types ofinterfaces in the transmission device, the terminal and the like, whichare to be connected.

[0203] In order to achieve the foregoing object, a switching device inthe optical transmission system according to the present inventioncomprises: a replaceable optical module capable of performingphotoelectric conversion or electric-optic conversion on inputted data;a CDR circuit being provided in correspondence with the data from theoptical module for reproducing data and clock at a timing according to aset rate; and a device information judging circuit for judging deviceinformation of the optical module through reading out type information,that is, information about the types of interface of the optical moduleand a transmission code in the interface, and for setting the rate ofthe CDR circuit through discriminating the interface rate.

[0204] The present invention is provided with the replaceable opticalmodule, the CDR circuit corresponding to multi-rate capable of settingthe rate, and the device information judging circuit having a functionof reading out the type of the interface of the optical module noted inthe optical module and for setting the rate according to the type of theinterface for the CDR circuit. Therefore, the type of the interface canbe automatically recognized and the rate is set for the CDR circuit.Thereby, it becomes possible to correspond to various types ofinterfaces by simply changing the optical module. Therefore, theswitching device can be used without being affected by the types of theinterfaces of the transmission device, the terminal and the like, whichare to be connected.

[0205] Also, another switching device in the optical transmission systemaccording to the present invention comprises: a first replaceableoptical module capable of performing photoelectric conversion oninputted data; a first CDR circuit for reproducing data and clock fromthe data from the first optical module at a timing according to a setrate; a first device information judging circuit for judging deviceinformation of the first optical module through reading out typeinformation, that is, information about the types of interface of thefirst optical module and a transmission code in the interface, and forsetting the rate of the first CDR circuit through discriminating theinterface rate; a branching circuit for branching data which iswaveform-shaped by the first CDR circuit into a plurality of systems; aplurality of second CDR circuits for reproducing, respectively, aplurality of data and clocks which are branched by the branching circuitat a timing according to a set rate; a plurality of replaceable secondoptical modules for performing electric-optic conversion on a pluralityof data which are waveform-shaped by the second CDR circuits; and aplurality of second device information judging circuits for judgingdevice information of a plurality of the second optical modules,respectively, through reading out type information, that is, informationabout the types of interface of a plurality of the second opticalmodules and a transmission code in the interface, respectively, and forsetting the rate of a plurality of the second CDR circuits throughdiscriminating the interface rate, respectively.

[0206] With the present invention, the switching device for branching adata to a plurality of system of data can be formed to have a structurewhich can correspond to various types of interfaces by simply changingthe optical module. Therefore, the switching device can be used withoutbeing affected by the transmission device, the terminal and the like,which are to be connected.

[0207] Also, still another switching device in the optical transmissionsystem according to the present invention comprises: a plurality offirst replaceable optical module, which is performing photoelectricconversion on inputted data each other; a plurality of first CDRcircuits for reproducing data and clock from a plurality of the firstoptical modules at a timing according to a set rate; a plurality offirst device information judging circuits for judging device informationof a plurality of the first optical modules, respectively, throughreading out type information, that is, information about the types ofinterface of a plurality of the first optical modules and a transmissioncode in the interface, respectively, and for setting the rate of aplurality of the first CDR circuits through discriminating the interfacerate, respectively; a selection circuit for selecting a system which canreceive an effective data through recognizing presence of a plurality ofsystems of data which are waveform-shaped by a plurality of the firstCDR circuits; a second CDR circuit for reproducing data and clock of thesystem selected by the selection circuit at a timing according to a setrate; a second optical module for performing electric-optic conversionon data which is waveform-shaped by the second CDR circuit; and a seconddevice information judging circuit for judging device information of thesecond optical module through reading out type information, that is,information about the types of interface of the second optical moduleand a transmission code in the interface, and for setting the rate ofthe second CDR circuit through discriminating the interface rate,respectively.

[0208] With the present invention, the switching device for selectingone of the data out of a plurality of the data can be formed to have astructure which can correspond to various types of interfaces by simplychanging the optical module. Therefore, the switching device can be usedwithout being affected by the transmission device, the terminal and thelike, which are to be connected.

[0209] Also, further another switching device in the opticaltransmission system according to the present invention comprises: aplurality of first replaceable optical modules capable of performingphotoelectric conversion on inputted data; a plurality of first CDRcircuits for reproducing data and clock from a plurality of the firstoptical modules at a timing according to a set rate; a plurality offirst device information judging circuits for judging device informationof a plurality of the first optical modules, respectively, throughreading out type information, that is, information about the types ofinterface of a plurality of the first optical modules and a transmissioncode in the interface, respectively, and for setting the rate of aplurality of the first CDR circuits through discriminating the interfacerate, respectively; a switching circuit for outputting data on aplurality of lines which are waveform-shaped by a plurality of first CDRcircuits to a recipient determined based on the line setting setbeforehand; a line setting circuit for performing line-switching on theswitching circuit based on a setting from outside; a plurality of secondCDR circuits for reproducing data and clocks on a plurality of linesoutputted from the switching circuit at a timing according to a setrate; and a plurality of second device information judging circuits forjudging device information of a plurality of the second optical modules,respectively, through reading out type information, that is, informationabout the types of interface of a plurality of the second opticalmodules and a transmission code in the interface, respectively, and forsetting the rate of a plurality of the second CDR circuits throughdiscriminating the interface rate, respectively.

[0210] With the present invention, the switching device which functionsas a cross-connecting device for performing switching between aplurality of the lines can be formed to have a structure which cancorrespond to various types of interfaces by simply changing the opticalmodule. Therefore, the switching device can be used without beingaffected by the transmission device, the terminal and the like, whichare to be connected.

[0211] Next, a specific example of the optical transmission switchingdevice according to the present invention will be described in detail.The optical transmission system according to the embodiment, as shown inFIG. 14, is a system in which the present invention is applied to theoptical transmission system employing a protection system as shown inFIG. 36.

[0212] The optical transmission system according to the embodimentcomprises a terminal (transmission side) 210, a switching device(transmission side) 295, transmission devices (transmission side) 212,215, transmission paths 213, 216, transmission devices (reception side)214, 217, a switching device (reception side) 275, and a terminal(reception side) 219.

[0213] In the optical transmission system according to the embodiment,the switching device 211 on the transmission side and the switchingdevice 218 on the reception side of the conventional opticaltransmission system shown in FIG. 36 are replaced with the switchingdevice 295 and the switching device 275, respectively.

[0214] The switching device 295 has a function that it can be usedwithout depending on the signal protocol and frame format of theterminal 210 and the transmission devices 212, 215, in addition tohaving the same function as the switching system 211 in the conventionaloptical transmission system shown in FIG. 36, which is to branch thedata from the terminal device 210 on the transmission side into two andtransmits the branched data to the transmission devices 212 and 215,respectively.

[0215] Further, the switching device 275 has a function that it can beused without depending on the signal protocol and frame format of theterminal 219 and the transmission devices 214, 217, in addition tohaving the same function as the switching system 218 in the conventionaloptical transmission system shown in FIG. 36, which is to select thedata from either the transmission device 214 or the transmission device217 to transmit the data to the terminal 219.

[0216] In the followings, the specific structure of the switchingdevices 295 and 275 will be described in detail by referring to FIG. 15and FIG. 16.

[0217] First, the switching device 295 corresponding to multi-rate shownin FIG. 14 comprises, as shown in FIG. 15, device information judgingcircuits 280, 283, 288, optical modules 281, 285, 287, CDR (Clock andData Recovery) circuits 282, 284, 286 and a two-branching circuit 282.

[0218] The optical module 281 has a structure to be replaceable andperforms photoelectric conversion to the data inputted from the terminal210. The CDR circuit 282 is a CDR circuit corresponding to multi-ratecapable of setting the rate, and is provided in correspondence with thedata from the optical module for reproducing data clock at a timingaccording to the set rate. In other words, the CDR circuit 282 performswaveform-shaping when the terminal 210 and the switching device 295 aredistant from each other.

[0219] The device information judging circuit 280 reads out the typeinformation of the optical module 281 from a register present in theoptical module 281, judges the device information of the optical module281, recognizes the interface rate and sets the rate for the CDR circuit282 through recovering clock from the data and performing waveformshaping. At this time, the type information of the optical moduleconsists of interface type and the information on the transmission code.

[0220] The two-branching device 290 branches the data waveform-shaped bythe CDR circuit into two systems of a present system and a standbysystem. The CDR circuits 284 and 286 have the same function as that ofthe CDR circuit 282, and reproduce the data and clock of the twosystems, respectively, which are branched by the two-branching device290 at a timing according to the rate set by the device informationjudging circuits 283 and 288.

[0221] The optical module 285 performs electric-optic conversion to thedata waveform-shaped by the CDR circuit 284 and then outputs it to thetransmission device 212. The optical module 287 performs electric-opticconversion to the data waveform-shaped by the CDR circuit 286 and thenoutputs it to the transmission device 215.

[0222] The device information judging circuit 288 reads out the typeinformation of the optical module 287 from a register present in theoptical module 287, judges the device information of the optical module287, recognizes the interface rate and sets the recognized interfacerate for the CDR circuit 286 through recovering clock from the data andperforming waveform-shaping. The device information judging circuit 283reads out the type information of the optical module 285 from a registerpresent in the optical module 285, judges the device information of theoptical module 285, recognizes the interface rate and sets the rate forthe CDR circuit 284 through recovering clock from the data and performswaveform-shaping.

[0223] The optical modules 281, 285, and 287 used in the system are theones that are replaceable by each module, and are connected to thedevices through a common connector. Examples of such modules are SFP(Small Form Factor Pluggable) optical module and GBIC (Gigabit InterfaceConnector) optical modules. It is on condition that these opticalmodules are used in the system. In the register present inside theoptical modules 281, 285, and 287, type information consisting of theinterface type and notification on the transmission code of theinterface is stored.

[0224] As shown in FIG. 15, the CDR circuits 284 and 285 are alsomounted on the output side so that the transmission path error bydeterioration of waveform can be reduced through transmitting data afterperforming waveform-shaping when the switching device 211 and thetransmission devices 212 and 215 shown in FIG. 14 are distant from eachother.

[0225] Next, the switching device 275 on the reception side, as shown inFIG. 16, comprises device information judging circuits 260, 265, 267,optical modules 261, 263, 269, CDR circuits 262, 264, 268 and aselection circuit 266.

[0226] The optical modules 261 and 263 perform photoelectric conversionto the data inputted from the transmission devices 214 and 217,respectively. The device information judging circuits 260 and 265 readout the type information of the optical modules 261 and 263 from theregister present in the optical modules 261 and 263, recognize thedevice information of the optical modules 261 and 263, recognizes theinterface rate, and set the rate for the CDR circuits 262 and 264,respectively. The CDR circuits 284 and 286 reproduce the data and clockfrom the optical modules 261 and 263, respectively, at a timingaccording to the rate set by the device information judging circuits 260and 267.

[0227] The selection circuit 266 judges the presence of data in twosystems, which are waveform-shaped by the CDR circuits 262 and 264, andselects the system from which valid data can be received. The CDRcircuit 268 reproduces the data and clock of the system selected by theselection circuit 266 at a timing according to the rate set by thedevice information judging circuit 267.

[0228] The optical module 269 performs electric-optic conversion to thedata waveform-shaped by the CDR circuit 268 and outputs it to theterminal 219. The device information judging circuit 267 reads out thetype information of the optical module 269 from the register present inthe optical module, recognizes the device information of the opticalmodule 269, recognizes the interface rate and sets the rate for the CDRcircuit 268.

[0229] Next, operation of the optical transmission system according tothe embodiment will be described in detail by referring to the drawings.

[0230] In the optical transmission system according to the embodimentshown in FIG. 14, only the operation of the switching devices 295 and275 is different from that in the conventional optical transmissionsystem shown in FIG. 36. Therefore, in the description provided below,the operation of the switching devices 295 and 275 will be described.

[0231] First, operation of the switching device 295 will be described indetail by referring to FIG. 15. In the switching device 295, the datainputted from the terminal 210 is received in the optical module 281.The state of mounting the optical module 281 and the type information ofthe mounted optical module 281 are monitored by the device informationjudging circuit 280 at all times and, when the optical module 281 isbeing replaced, the reception side is aligned through changing the setrate value for the CDR circuit 282. As the method for setting the ratefor the CDR circuit 282, the device information judging circuit 280maybe provided with a function of setting the rate by hardware orsoftware. It is possible to select a setting method using hardware inwhich the type of the optical module 281 is recognized and, when thereis a change in the module, changes the setting, or to select a methodusing software in which an operator sets the rate from the controlterminal. In the description of the device information judging circuits280, 283, 288, 260, 265 and the like provided below, it is provided oncondition that each device information judging circuit is provided withthis function.

[0232] The process of the interface rate setting method will be shown inthe flowchart in FIG. 17. First, the device information judging circuitjudges whether or not the optical module is mounted (step 250). When nomodule is mounted, the device does not set the rate and monitors themounting notification until a module is mounted. When it is judged inthe step 250 that a module is mounted, the device information judgingcircuit reads out information inside the optical module (step 252) andjudges the device information using a prescribed table. For example, ifthe optical module is SFP, the type and the rate of the interface arerecognized (step 252) by referring to the address 4 h to Bh (h: denoteshexadecimal) of the inside register using the table as shown in FIG. 18.For example, when data of the addresses 4 h, 5, 7 h to Ah are 0 h anddata of 6 h is 1 h, it means 1000 BASE-SX interface of Gigabit Ethernet,which is the interface having a transmission capacity of 1G bit/sec.

[0233] Further, transmission codes of the interfaces can be identifiedthrough referring to the address Bh as they are shown in the tableshowing the SFP transmission code type in FIG. 19. For example, if 01 his read out, the SFP transmission code is identified as 8B10B, the rateof the interface is identified as 10/8 times the transmission capacitythereby to be 1.25 G bit/sec. When the rate of the interface isidentified, the setting of the rate for the CDR circuit 282 isperformed.

[0234] The signal waveform-shaped by the CDR circuit 282 shown in FIG.15 is then branched into the signals for the present system line and thestandby system line by the two-branching circuit 282. The signals arethen inputted to the CDR circuits 284 and 286. As for the opticalmodules 285 and 287 mounted on the output side, as in the same manner asthat of the input side, the type information of the mounted opticalmodules is read out by the device information judging circuits 283 and288 and rate setting for the CDR circuits 284 and 286 is performed.Basically, the interfaces on the input side and the output side are thesame. Thus, unless it has a duplex structure, the terminal 210 and thetransmission device 212 shown in FIG. 14 are directly connected so thatthe input/output rate and the interface condition coincide with eachother.

[0235] The data outputted from the optical modules 285 and 287 shown inFIG. 15 are outputted to the transmission devices 212 and 215 shown inFIG. 14 and then are transmitted to the transmission devices 214 and 217via the transmission path 213 and the transmission path 216. Theoperation of the transfer method of the fault is as same as that of themethod described by referring to FIG. 36. The fault in the transmissionpath is detected when the signal to the switching device 275 isinterrupted and the line is switched to the system in which no fault isgenerated.

[0236] Next, operation of the switching device 275 will be described indetail by referring to FIG. 16. In the switching device 275, the datainputted from the transmission devices 214 and 217 shown in FIG. 14 arereceived in the optical modules 261 and 263. The device informationjudging circuits 260 and 265 read out the type information of theoptical modules 261 and 263 and set the rate for the CDR circuits 262and 264. The selection circuit 266 monitors the loss of the input signaland, when the input signal of the system selected at present isinterrupted, switch the line to the other system. For example, if thesystem selected at present is the input from the CDR circuit 262, thedevice monitors the reception state of the signal on the CDR circuit 264side. When the input signal is not interrupted, the device switch theselection system to the CDR circuit 262 side.

[0237] The signal selected by the selection circuit 266 is inputted tothe CDR circuit 268, then is waveform-shaped and outputted to theoptical module 269. The device information judging circuit 267 reads outthe type information of the optical module 269 and sets the rate for theCDR circuit 268. The CDR circuits 262 and 264 are provided so as toreduce the transmission path error due to deterioration of the waveformby waveform-shaping when the transmission devices 214 and 217 shown inFIG. 14 are distant form each other. Also, the CDR circuit 268 isprovided so as to reduce the transmission path error due todeterioration of the waveform by waveform-shaping when the switchingdevice 275 and the terminal 219 are distant form each other.

[0238] In the switching devices 295 and 275 in the optical transmissionsystem according to the embodiment, the optical modules 281, 285, 287,261, 263, and 269 have a structure to be replaceable. Therefore, it ispossible to select and mount the one to coincide with the each interfaceof the device to be connected. The device information judging circuits280, 283, 288, 260, 265 and 267 provided in the switching devices 295and 275 judges the types of the mounted optical modules, respectively,and recognize the interface rate thereby to automatically performsetting of the rate for the CDR circuits 282, 285, 287, 262, 264 and268. Therefore, in the switching devices 295 and 275 according to theembodiment, only the optical module part is being replaced to coincidewith each interface so that it becomes unnecessary to design a switchingdevice specifically for the device interface. In other words, as fordeveloping the device, it can achieve a system in which one kind of thedevice is developed and decide the interface according to the opticalmodule to be mounted on the interface part of the device.

[0239] Next, another optical transmission system according to theembodiment of the present invention will be described by referring toFIG. 20. The difference between the embodiment shown in FIG. 14 and theembodiment shown in FIG. 20 is that one device is provided on theterminal side and two systems are provided on the transmission path sidein the former whereas, in the latter, a plurality of terminals (twoterminals in this case) are provided through performing cross connectionby a switching device thereby to correspond to a network in which thetransmission path differs by every terminal.

[0240] The optical transmission system according to the embodiment asshown in FIG. 20 comprises two transmission-side terminals 210-1, 210-2,a transmission side switching device 220, transmission-side transmissiondevices 212, 215, transmission oaths 213, 216, two reception-sidetransmission devices 214, 217, reception-side switching device 221, tworeception-side terminals 219-1, 219-2, and line setting terminals 222,223.

[0241] Two terminals, the terminal 210-1 and the terminal 210-2 areconnected to the switching device 220 on the transmission side. The linesetting terminal 222 for setting which transmission path to be used forconnecting the terminal is connected to the switching device 220. Theline connection on the transmission side is set by the line settingterminal 220. The transmission device 212 and the transmission device215 are connected to the transmission side of the switching device 220and data is transmitted to the transmission device 214 and thetransmission device 217 via the transmission path 213 and thetransmission path 216. A switching device 221 is connected to the outputside of the transmission devices 214 and 217. The switching device 221has a function of transferring data to the two terminals 219-1 and219-2, and is capable of deciding the connection between thetransmission paths and the terminals (which one to which) based on thesetting by the line setting terminal 223.

[0242] The switching devices 295 and 275 in the optical transmissionsystem according to the former embodiment shown in FIG. 14 function as aprotection switch for the line with duplex structure. However, theswitching devices 220 and 221 according to the present embodimentfunction as a cross-connecting device for switching a plurality oflines.

[0243] Next, FIG. 21 shows the configuration of the switching device 220shown in FIG. 20. The switching device 220 functioning as a multi-ratecross-connecting device has a configuration in which: with respect tothe switching device 295 corresponding to the multi-rate as shown inFIG. 15, an optical module 224, a CDR circuit 225 and a deviceinformation judging circuit 226 are added for corresponding to theadditional connection to the terminal 210-2; the two-branching device290 shown in FIG. 15 is replaced with the switching circuit 231; and aline setting circuit 230 is added for performing line switching to theswitching circuit 231 based on the setting by the line setting terminal222.

[0244] The optical module 224, the CDR circuit 225, and the deviceinformation judging circuit 226 have the same function as that of theoptical module 281, the CDR circuit 282 and the device informationjudging circuit 280, respectively. The switching circuit 231 outputs thedata waveform-shaped by the CDR circuits 282 and 225 to the designatedpart which is determined based on the line setting set by the linesetting circuit 230.

[0245] Next, FIG. 22 shows the configuration of the switching device 221shown in FIG. 20. The switching device 221 functioning as a multi-ratecross-connecting device has a configuration in which: with respect tothe switching device 275 corresponding to the multi-rate as shown inFIG. 16, an optical module 235, a CDR circuit 234 and a deviceinformation judging circuit 236 are added for corresponding to theadditional connection to the terminal 219-2; the selection circuit 266shown in FIG. 16 is replaced with the switching circuit 233; and a linesetting circuit 232 is added for performing line switching to theswitching circuit 233 based on the setting by the line setting terminal223.

[0246] The optical module 234, the CDR circuit 235, and the deviceinformation judging circuit 236 have the same function as that of theoptical module 269, the CDR circuit 268 and the device informationjudging circuit 267, respectively. The switching circuit 233 outputs thedata waveform-shaped by the CDR circuits 262 and 264 to the designatedpart which is determined based on the line setting set by the linesetting circuit 232.

[0247] First, operation of the switching device will be described byreferring to FIG. 21. In the switching device 220, data inputted fromthe terminals 210-1 and 210-2 interface with the optical modules 281 and224. The device information judging circuit 280 and 226 judge the typesof the optical modules 281 and 224, respectively, and set the rate forthe CDR circuit 282 and 225. The output from the CDR circuits 282 and225 is inputted to the switching circuit 231. In the switching circuit231, the designated switch to which the data inputted from the CDRcircuits 282 and 225 is outputted is determined based on the linesetting set by the line setting circuit 230.

[0248] On the output side of the switching circuit 231, the interfacerate is set in the device information judging circuits 283 and 288,which recognize the types of the optical modules 285, 287 provided onthe transmission path side for performing setting of the rate for theCDR circuits 284 and 286. The CDR circuits 284 and 286 have a functionof waveform-shaping the output data. The data outputted from the opticalmodules 285 and 287 are outputted to the transmission paths 213 and 216,respectively, via the transmission device 212 and the transmissiondevice 215 shown in FIG. 20.

[0249] Next, operation of the switching device 212 will be described byreferring to FIG. 22. In the switching device 221, data from thetransmission paths 213 and 216 are transmitted via the transmissiondevices 214, 217 and interface with the optical modules 261 and 263. Thedevice information judging circuit 260 and 265 recognize the types ofthe optical modules 261 and 263, respectively, and set the rate for theCDR circuit 262 and 264. The output from the CDR circuits 262 and 264 isinputted to the switching circuit 233. In the switching circuit 233, thedesignated switch to which the data inputted from the CDR circuits 262and 264 is inputted is determined based on the line setting set by theline setting circuit 232.

[0250] On the output side of the switching circuit 233, the interfacerate is set in the device information judging circuits 267 and 236,which judge the types of the optical modules 269 and 235 provided on theterminal side for performing setting of the rate for the CDR circuits268 and 234. The CDR circuits 268 and 234 have a function ofwaveform-shaping the output data. The data outputted from the opticalmodules 269 and 235 are outputted to the terminals 219-1 and 219-2 shownin FIG. 20.

[0251] In the embodiment, the switching circuits 231 and 233 providedinside the switching device 221 and 221 have a 2×2 structure with twoinput channels and two output channels. However, the present inventionis not limited to this and, generally, can achieve the same functioneven when it is extended to the n×n switch with n input channels and noutput channels.

[0252] In the embodiment, the switching device is not for duplexswitching but is to have a structure capable of achievingcross-connecting function. With this structure, it is also possible tocorrespond to the interfaces with different interface rates by simplyreplacing the optical modules. It is possible to correspond to the ratesby simply replacing the optical modules to change the interface withoutchanging the interface part of the cross-connecting device.

[0253] In the embodiment described above, the present invention isapplied, respectively, to a switching device for branching a data into aplurality of systems of data, a switching device for selecting onesystem out of a plurality of the system of data, and a switching devicefor switching between a plurality of the lines. However, the presentinvention is not limited to such a case but is applicable to switchingdevices with other configurations as well. In such a case, the sameeffects can be achieved by having at least one configuration with anoptical module, a CDR circuit and a device information judging circuit.

[0254] Furthermore, the embodiment has been described by referring tothe case with the register present in the optical module and the typeinformation of the optical module is stored in the register. However,the present invention is not limited to such a case but is applicable toany configuration as well, as long as it is a configuration in which thetype information can be read out from outside.

[0255] As described, with the optical transmission switching deviceaccording to the present invention, the switching device for branching adata into a plurality of systems of data, a switching device forselecting a data out of a plurality of systems of the data, and aswitching device for switching a plurality of lines can be formed to becapable of corresponding to various interfaces by simply replacing theoptical module. Thus, the switching device can be used without beingaffected by the transmission devices, the terminals and the like, whichare to be connected.

[0256] Next, the multiplex communication system according to the presentinvention to which the above-described line switching system, theoptical transmission switching devices and the like can be applied willbe described. In order to provide a distinctive feature of the multiplexcommunication system according to the present invention, it will bedescribed by making a comparison to a conventional case.

[0257] As has been described, in order to improve the reliability of themultiplex communication system, a system is built in which duplextransmission paths of an active system and a standby system are providedthereby to switch the system to the standby system when there is a faultgenerated in the transmission path of the active system.

[0258] As the communication system, various types of protocols have beenused, in which the active system is switched to the standby system whenthe transferred alarm is recognized by using a protocol having an alarmtransfer function for generating and transferring the alarm when a faultis generated in the transmission path.

[0259] Further, the switching part for switching the active system andthe standby system is combined with a multiplex device for performingmultiplexing, thereby to perform multiplexing/separation of signals andswitching between the active system and the standby system under acontrol by the same control part.

[0260] The transmission path duplex system of the conventional multiplexcommunication device described above is achieved on condition that ituses a protocol having the alarm transfer function. Therefore, it cannotbe applied to a communication system using a data communication protocolin which no alarm transfer function is defined like, e.g., Ethernet.

[0261] Also, when the alarm transfer function is used, the system cannotbe switched to the standby system until the alarm transfer is completed.Thus, there faces a problem that the switching cannot be performedpromptly.

[0262] Further, the switching part and the multiplex devices are unifiedinto one body so that the user lines are connected to the multiplexdevice via the switching device. Therefore, the scale of the devicebecomes large and the price is increased.

[0263] Also, it has a configuration in which the line connected to theswitching part is duplicated inside the device to be connected to themultiplex device. Therefore, in the case where there are a service forduplicating the transmission line and a service without duplicating thetransmission path being provided together, the line of the user, thatdoes not require the duplex service (single line service), is alsoduplicated to be connected. Thus, the channels to be multiplexed cannotbe effectively utilized.

[0264] The present invention has been designed to overcome the foregoingproblems present in the related art as described. An object is toperform a prompt switching of the transmission paths in any types of theprotocols and to achieve a multiplex communication system which caneffectively utilize the channel to be multiplexed.

[0265] In order to achieve the foregoing object, the multiplexcommunication system according to the present invention comprises aswitching device for duplicating data on a plurality of transmissionpaths thereby to distribute the data to an active system transmissionpath and a standby system transmission path; and a multiplex deviceprovided on each of the active system transmission path and the standbysystem transmission path for multiplexing data which are distributed bythe switching device and transmitted via the transmission paths. Acontrol part is provided in each of the switching device and themultiplex device, and each of the control part together switches thetransmission path from the active system to the standby system upondetecting a fault in the transmission path based on a state that no datasigned is transmitted via each transmission path.

[0266] In this case, the multiplex device may comprise: a plurality oflow-speed transmission/reception parts connected to a switching device;a multiplex part for multiplexing data received in the low-speedtransmission/reception part; a high-speed transmission/reception partfor outputting multiplex data multiplexed by the multiplex part toanother opposing multiplex device; a separation part for separating themultiplex data from the opposing multiplex device received in thehigh-speed transmission/reception part and outputting the separated datato a plurality of the low-speed transmission/reception parts; and acontrol part for controlling operation of each part. Each of thelow-speed transmission/reception parts and the high-speedtransmission/reception part may notify an input fault to the controlpart and interrupt output of signal when input of signal from thetransmission path connected to the multiplex device is interrupted for aprescribed time or longer; and the control part, upon receiving thenotification, may interrupt the output signal of the low-speedtransmission/reception parts or the high-speed transmission/receptionpart to which the fault has not been notified.

[0267] In any case described above, the switching device may comprise: aplurality of first low-speed transmission/reception parts connected to aplurality of transmission paths, respectively; a plurality of second andthird low-speed transmission/reception parts connected to the multiplexdevice provided on the active system and standby system transmissionpaths, respectively, corresponding to a plurality of the low-speedtransmission/reception parts; a copy/selection part provided in betweenthe first low-speed transmission/reception parts and the second andthird low-speed transmission/reception parts, for copying data from thefirst low-speed transmission/reception parts and outputting the data tothe second and third low-speed transmission/reception parts, and forselecting data either from the second or third low-speedtransmission/reception part and outputting it to the first low-speedtransmission/reception parts; and a control part for controllingoperation of each part. Also, each of the second and third low-speedtransmission/reception part may notify an input fault to the controlpart when input of signal from the transmission path connected to themultiplex device is interrupted for a prescribed time or longer; and thecontrol part, upon receiving the notification, may make thecopy/selection part select the data from the second low-speedtransmission/reception part in a normal state and, when notified of aninput fault from the second low-speed transmission/reception part, maymake the copy/selection part select the data from the third low-speedtransmission/reception part after confirming that there is nonotification about an input fault from the third low-speedtransmission/reception part for a prescribed time or longer.

[0268] Further, the copy/selection part may comprise: a copy part forcopying data from the first low-speed transmission/reception parts tooutput the data to the second and third low-speed transmission/receptionparts and a selection part for selecting the data either from the secondor third low-speed transmission/reception part to output it to the firstlow-speed transmission/reception parts. Also, the copy/selection partmay be a switch comprising a plurality of input/output ports.

[0269] In the multiplex communication system according to the presentinvention with the configuration as described, when detecting a fault inthe transmission path, a prompt switching of the transmission path isachieved through notifying the transmission path fault on both ends ofthe duplex structure section by utilizing interruption of the opticaloutput.

[0270] It is a distinctive feature of the system that, by separating theduplex switching function and the multiplex function, the transmissionduplex service and the transmission single line service can be providedat the same time and the number of the stored lines can be increased.

[0271] Also, the multiplex device and the switching device are separatedand the switching device side performs detection of the non-input-signedstate without terminating the transmission frame individually by everychannel (ch) to be stored. Therefore, the switching device itself doesnot depend on the communication protocol.

[0272] It is also a distinctive feature that it is possible to use adifferent protocol by a channel (ch) unit inside a switching device.

[0273] It is another distinctive feature that a different transmissionpath to be duplicated can be selected individually by every channel (ch)so that it is more widely applicable than the case in which the duplexswitching part is provided inside the multiplex device. In the system,interruption of the optical input/output is utilized, however,interruption of the input/output of the electric signals can be alsoutilized in the same system.

[0274] A specific example of the multiplex communication systemaccording to the present invention will be described in the followingsby referring to FIG. 23 to FIG. 25. It is shown separately in FIG. 23,FIG. 24 and FIG. 25 due to the available space. However, the terminalsT1˜T16 and the opposing terminals T1′˜T16′ in FIG. 23 and FIG. 24 areconnected to each other and the terminals T1˜T16 and the opposingterminals T1′˜T16′ in FIG. 24 and FIG. 25 are also connected to eachother thereby to build the multiplex system according to the embodimentof the present invention.

[0275] The Example as shown in FIG. 23 to FIG. 25 comprises twoswitching devices 301, 306, four multiplex devices 302, 303, 304, 305,and lines for connecting each device. The two switching devices 301 and306, and the four multiplex devices 302, 303, 304 and 306 have the sameconfiguration, respectively. The transfer between each switching deviceis performed in the multiplex devices 302 to 305 provided in between theswitching devices 301 and 306. The multiplex devices 302 and 304 formthe 0-system high-speed transmission path as one of the transmissionpath and the multiplex devices 303 and 305 form the 1-system high-speedtransmission path as the other transmission path.

[0276] In the Example, as described above, the multiple number by themultiplex device is set to be 4. However, the present invention isapplicable as long as the multiple factor is any integer of 1 or larger.

[0277] First, the configuration of the switching devices 301 and 302will be described in detail. The switching device 301 compriseslow-speed transmission/reception parts 301-1 to 301-4, 304-0-1 to304-0-4, 304-1-1 to 304-1-4, COPY parts 302-1 to 302-4, SEL part(selection part) 303-1 to 303-4, and a control part 305 which isconnected to each of the parts for controlling the operation.

[0278] The low-speed transmission/reception parts 301-1 to 301-4 areconnected to low-speed lines 301 a to 304 a which serve as theconnection lines between the outside-of the switching device 301. Also,the low-speed transmission/reception parts 301-1 to 301-4 are connectedto the COPY parts 302-1 to 302-4 and the SEL parts 303-1 to 303-4,respectively, inside the switching device 301, and have a bi-directionalconversion function for the optical signals on the low-speed lines 301 ato 304 a and the electric signals inside the switching device 301.Further, the low-speed transmission/reception parts 301-1 to 301-4 havea function of monitoring the signal inputted from the low-speed lines301 a to 304 a, and notifying a fault in the input signal to the controlpart 305 when there is a fault such as the non-input-signed state beingcontinued for a prescribed time or longer. Also, the low-speedtransmission/reception parts 301-1 to 301-4 have a function ofinterrupting the optical output to the low-speed lines 301 a to 304 aaccording to the output control signal inputted from the control part305.

[0279] The COPY parts 302-1 to 302-4 have a function of copying thesignals inputted from the low-speed transmission/reception parts 301-1to 301-4 and outputting the copies to the low-speedtransmission/reception parts 304-0-1 to 304-0-4 and 304-1-1 to 304-1-4,respectively.

[0280] The SEL parts 303-1 to 303-4 have a function of inputting thesignals from each of the low-speed transmission/reception parts 304-0-1to 304-0-4 and 304-1-1 to 304-1-4 and selecting any of the input signalsaccording to the selection signal inputted from the control part 305thereby to output the selected signal to the low-speedtransmission/reception parts 301-1 to 301-4.

[0281] The low-speed transmission/reception parts 304-0-1 to 304-0-4,304-1-1 to 304-1-4 are connected to the COPY parts 302-1 to 302-4 andthe SEL parts 303-1 to 303-4 inside the switching device 301. Also, thelow-speed transmission/reception parts 301-1 to 301-4 and 304-1-1 to304-1-4 are connected to the multiplex devices 302 and 303 via thelow-speed transmission paths 301 a-0 to 304 a-0 and 301 a-1 to 304 a-1,provided respectively in between the multiplex devices 302 and 303,while having a bi-directional conversion function for the electricsignal inside the switching device 301 and the optical signals on thelow-speed transmission paths 301 a-0 to 304 a-0 and 301 a-1 to 304 a-1.Further, the low-speed transmission/reception parts 304-0-1 to 304-0-4and 304-1-1 to 304-1-4 have a function of monitoring the signal inputtedfrom low-speed transmission paths 301 a-0 to 304 a-0 and 301 a-1 to 304a-1, and notifying a fault in the input signal to the control circuit305 when there is a fault such as the non-input-signed state of theinput signal being continued for a prescribed time or longer. Also, thelow-speed transmission/reception parts 304-0-1 to 304-0-4, and 304-1-1to 304-1-4 have a function of interrupting the optical output to thelow-speed transmission paths 301 a-0 to 304 a-0, 301 a-1 to 304 a-1according to the output control signal inputted from the control part305.

[0282] The control part 305 have a function of controlling opticaloutput of each low-speed transmission/reception part and controlling theselection in the SEL parts 303-1 to 303-4 through monitoring the inputfault signals by every channel, showing the fault in the input signalsinputted from each of the low-speed transmission/reception parts 301-1to 301-4 and the low-speed transmission/reception parts 304-0-1 to304-0-4 and 304-1-1 to 304-1-4.

[0283] The switching device 306 has the same configuration as that ofthe switching device 301. The low-speed transmission/reception parts317-1 to 317-4, 314-0-1 to 314-0-4 and 314-1-1 to 314-1-4 of theswitching device 306 correspond to the low-speed transmission/receptionparts 301-1 to 301-4, 304-0-1 to 304-0-4, and 304-1-1 to 304-1-4 of theswitching device 301, respectively. Also, the COPY parts 315-1 to 315-4,the SEL parts 316-1 to 316-4, and the control part 318 of the switchingdevice 306 correspond to the COPY parts 302-1 to 302-4, the SEL parts303-1 to 303-4 and the control part 305 of the switching device 301,respectively.

[0284] The low-speed transmission/reception parts 317-1 to 317-4 areconnected to low-speed lines 301 b to 304 b as the connection linesbetween the outside of the switching device 306. Also, the low-speedtransmission/reception parts 317-1 to 317-4 are connected to the COPYparts 316-1 to 316-4 and the SEL parts 315-1 to 315-4, respectively,inside the switching device 306, while having a bi-directionalconversion function for the optical signals on the low-speed lines 301 bto 304 b and the electric signals inside the switching device 306.Further, the low-speed transmission/reception parts 317-1 to 317-4 havea function of monitoring the signal inputted from the low-speed lines301 b to 304 b, and notifying a fault in the input signal to the controlpart 318 when there is a fault such as the non-input-signal state beingcontinued for a prescribed time or longer. Also, the low-speedtransmission/reception parts 317-1 to 317-4 have a function ofinterrupting the optical output to the low-speed lines 301 b to 304 baccording to the output control signal inputted from the control part318.

[0285] The COPY parts 316-1 to 316-4 have a function of copying thesignals inputted from the low-speed transmission/reception parts 317-1to 317-4 and outputting the copies to the low-speedtransmission/reception parts 314-0-1 to 314-0-4 and 314-1-1 to 314-1-4,respectively.

[0286] The SEL parts 315-1 to 315-4 have a function of inputting thesignals from each of the low-speed transmission/reception parts 314-0-1to 314-0-4 and 314-1-1 to 314-1-4 and selecting any of the outputsignals according to the selection signal inputted from the control part318 thereby to output the selected signal to the low-speedtransmission/reception parts 317-1 to 317-4.

[0287] The low-speed transmission/reception parts 314-0-1 to 314-0-4,314-1-1 to 314-1-4 are connected to the COPY parts 316-1 to 316-4 andthe SEL parts 315-1 to 315-4 inside the switching device 306. Also, thelow-speed transmission/reception parts 314-0-1 to 314-0-4 and 314-1-1 to314-1-4 are connected to the multiplex devices 304 and 305 via thelow-speed transmission paths 301 b-0 to 304 b-0 and 301 b-1 to 304 b-1,provided respectively in between the multiplex devices 304 and 305,while having a bi-directional conversion function for the electricsignal inside the switching device 306 and the optical signals on thelow-speed transmission paths 301 b-0 to 304 b-0 and 301 b-1 to 304 b-1.Further, the low-speed transmission/reception parts 314-0-1 to 314-0-4,and 314-1-1 to 314-1-4 have a function of monitoring the signal inputtedfrom low-speed transmission paths 301 b-0 to 304 b-0, 301 b-1 to 304b-1, and notifying a fault in the input signal to the control part 318when there is a fault such as the non-input-signed state being continuedfor a prescribed time or longer. Also, the low-speedtransmission/reception parts 314-0-1 to 314-0-4, and 314-1-1 to 314-1-4have a function of interrupting the optical output to the low-speedtransmission paths 301 b-0 to 304 b-0 and 301 b-1 to 304 b-1 accordingto the output control signal inputted from the control part 318.

[0288] The control part 318 have a function controlling optical outputof each low-speed transmission/reception part and controlling theselection in the SEL parts 315-1 to 315-4 through monitoring the inputfault signals by every channel, showing the fault in the input signalsinputted from each of the low-speed transmission/reception parts 317-1to 317-4 and the low-speed transmission/reception parts 314-0-1 to314-0-4 and 314-1-1 to 314-1-4.

[0289] Next, the configuration of the multiplex devices 302 to 305 willbe described in detail.

[0290] The multiplex device 302 comprises low-speedtransmission/reception parts 305-0-1 to 305-0-4, a MUX part 306-0, aDMUX part 307-0, a high-speed transmission/reception part 308-0, and acontrol part 309-0 being connected to each of the parts for controllingthe operation.

[0291] The low-speed transmission/reception parts 305-0-1 to 305-0-4 areconnected to the low-speed transmission/reception parts 304-0-1 to304-0-4 of the switching device 301, respectively, via the low-speedtransmission paths 301 a-0 to 301 a-4. The low-speedtransmission/reception parts 305-0-1 to 305-04 are also connected to theMUX part 306-0 and the DMUX part 307-0 inside the multiplex device 302,while having a bi-directional conversion function for the opticalsignals on the low-speed transmission paths 301 a-0 to 304 a-0 and theelectric signal inside the multiplex device 302. Further, the low-speedtransmission/reception parts 305-0-1 to 305-0-4 have a function ofmonitoring the signal inputted from low-speed transmission paths 301 a-0to 304 a-0, and notifying a fault in the input signal to the controlpart 309-0 when there is a fault such as the non-input signal statebeing continued for a prescribed time or longer. Also, the low-speedtransmission/reception parts 305-0-1 to 305-0-4 have a function ofinterrupting the optical output to the low-speed transmission paths 301a-0 to 304 a-0 according to the output control signal inputted from thecontrol part 309-0.

[0292] The MUX part 306-0 multiplexes the signal inputted from thelow-speed transmission/reception parts 305-0-1 to 305-0-4 and outputsthe signals to the high-speed transmission/reception part 308-0. Also,it has a function of inserting a transmission path fault detectionpattern showing the fault by every channel according to an instructionfrom the control part 309-0.

[0293] The DMUX part 307-0 separates the signals which are inputted fromthe high-speed transmission/reception part 308-0 by channel unit andthen outputs it to the low-speed transmission/reception parts 305-0-1 to305-0-4 of the corresponding channel. Also, it has a function ofdetecting the transmission path fault detection pattern showing thefault of each channel and notifying the fault to the control part 309-0.

[0294] The high-speed transmission/reception part 308-0 is provided inbetween the MUX part 306-0, the DMUX part 307-0, and the high-speedtransmission path 0, and has a bi-directional conversion function forthe optical signal on the high-speed transmission path 0 and theelectric signal inside the device. Also, the high-speedtransmission/reception part 308-0 has a function of monitoring thesignal inputted from the high-speed transmission path 0 and notifyingthe input fault to the control part 309-0 when detecting the fault.Further, it has a function of notifying the input fault to the opposingdevice through the high-speed transmission path 0. Furthermore, it has afunction of interrupting the optical output to the high-speedtransmission path 0 according to the output control signal inputted fromthe control part 309-0.

[0295] The control part 309-0 has a function of monitoring the inputfault signals inputted from the low-speed transmission/reception parts305-0-1 to 305-0-4, the high-speed transmission/reception part 308-0 andthe DMUX part 307-0 and performing the output control of the low-speedtransmission/reception parts 305-0-1 to 305-0-4 and the output controlof the high-speed transmission/reception part 308-0.

[0296] Each of the multiplex devices 303 to 305 has the sameconfiguration as that of the multiplex device 302. The low-speedtransmission/reception parts 305-1-1 to 305-1-4, 312-0-1 to 312-0-4, and312-1-1 to 312-1-4 in each of the multiplex devices 303 to 305correspond to the low-speed transmission/reception part 305-0-1 to305-0-4 in the multiplex device 302. Also, the MUX parts 306-1, 310-0,310-1, and the DMUX parts 307-1, 311-0, 311-1, the high-speedtransmission/reception parts 308-1, 314-0, 314-1, and the control parts309-1, 313-0, 313-1 in each of the multiplex devices 303 to 305correspond to the MUX part 306-0, the DMUX part 307-0, the high-speedtransmission/reception part 308-0 and the control part 309-0 in themultiplex device 302, respectively.

[0297] Each of the low-speed transmission/reception parts 305-1-1 to305-1-4 in the multiplex device 303 is connected to the low-speedtransmission/reception parts 304-1-1 to 304-1-4 of the switching device301 via the low-speed transmission paths 301 a-1 to 304 a-1. Also, thelow-speed transmission/reception parts 305-1-1 to 305-1-4 are connectedto the MUX part 306-1 and the DMUX part 307-1, respectively, inside themultiplex device 303, while having a bi-directional conversion functionfor the optical signals on the low-speed transmission paths 301 a-1 to304 a-1 and the electric signals inside the multiplex device 303.Further, the low-speed transmission/reception parts 305-1-1 to 305-1-4have a function of monitoring the signal inputted from the low-speedtransmission paths 301 a-1 to 304 a-1, and notifying a fault in theinput signal to the control part 309-1 when there is a fault such as thenon-input-signed state being continued for a prescribed time or longer.Also, the low-speed transmission/reception parts 305-1-1 to 305-1-4 havea function of interrupting the optical output to the low-speedtransmission paths 301 a-1 to 304 a-1 according to the output controlsignal inputted from the control part 309-1.

[0298] The MUX part 306-1 multiplexes the signal inputted from thelow-speed transmission/reception parts 305-1-1 to 305-1-4 and outputsthe signals to the high-speed transmission/reception part 308-1. Also,it has a function of inserting a transmission path fault detectionpattern showing the fault by every channel according to an instructionfrom the control part 309-1.

[0299] The DMUX part 307-1 separates the signals which are inputted fromthe high-speed transmission/reception part 308-1 by channel unit andthen outputs it to the low-speed transmission/reception parts 305-1-1 to305-1-4 of the corresponding channel. Also, it has a function ofdetecting the transmission path fault detection pattern showing thefault of each channel and notifying the fault to the control part 309-1.

[0300] The high-speed transmission/reception part 308-1 is provided inbetween the MUX part 306-1, the DMUX part 307-1, and the high-speedtransmission path 1, and has a bi-directional conversion function forthe optical signal on the high-speed transmission path 1 and theelectric signal inside the device. Also, the high-speedtransmission/reception part 308-1 has a function of monitoring thesignal inputted from the high-speed transmission path 1 and notifyingthe input fault to the control part 309-1 when detecting the fault.Further, it has a function of notifying the input fault to the opposingdevice through the high-speed transmission path 1. Furthermore, it has afunction of interrupting the optical output to the high-speedtransmission path 1 according to the output control signal inputted fromthe control part 309-1.

[0301] The control part 309-1 has a function of monitoring the inputfault signals inputted from the low-speed transmission/reception parts305-1-1 to 305-1-4, the high-speed transmission/reception part 308-1 andthe DMUX part 307-1, and performing the output control of the low-speedtransmission/reception parts 305-1-1 to 305-1-4 and the output controlof the high-speed transmission/reception part 308-1.

[0302] Each of the low-speed transmission/reception parts 312-0-1 to312-0-4 in the multiplex device 304 is connected to the low-speedtransmission/reception parts 304-0-1 to 304-0-4 of the switching device306 via the low-speed transmission paths 301 b-0 to 304 b-0. Also, thelow-speed transmission/reception parts 312-0-1 to 312-0-4 are connectedto the MUX part 311-0 and the DMUX part 310-0, respectively, inside themultiplex device 304, while having a bi-directional conversion functionfor the optical signals on the low-speed transmission paths 301 b-0 to304 b-0 and the electric signals inside the multiplex device 304.Further, the low-speed transmission/reception parts 312-0-1 to 312-0-4have a function of monitoring the signal inputted from the low-speedtransmission paths 301 b-0 to 304 b-0, and notifying a fault in theinput signal to the control part 313-0 when there is a fault such as thenon-input-signed state being continued for a prescribed time or longer.Also, the low-speed transmission/reception parts 312-0-1 to 312-0-4 havea function of interrupting the optical output to the low-speedtransmission paths 301 b-0 to 304 b-0 according to the output controlsignal inputted from the control part 313-0.

[0303] The MUX part 311-0 multiplexes the signal inputted from thelow-speed transmission/reception parts 312-0-1 to 312-0-4 and outputsthe signals to the high-speed transmission/reception part 314-0. Also,it has a function of inserting a transmission path fault detectionpattern showing the fault by every channel according to an instructionfrom the control part 313-0.

[0304] The DMUX part 310-0 separates the signals which are inputted fromthe high-speed transmission/reception part 314-0 by channel unit andthen outputs it to the low-speed transmission/reception parts 312-0-1 to312-0-4 of the corresponding channel. Also, it has a function ofdetecting the transmission path fault detection pattern showing thefault of each channel and notifying the fault to the control part 313-0.

[0305] The high-speed transmission/reception part 314-0 is provided inbetween the MUX part 311-0, the DMUX part 310-0, and the high-speedtransmission path 0, and has a bi-directional conversion function forthe optical signal on the high-speed transmission path 0 and theelectric signal inside the device. Also, the high-speedtransmission/reception part 314-0 has a function of monitoring thesignal inputted from the high-speed transmission path 0 and notifyingthe input fault to the control part 313-0 when detecting the fault suchas the non-input-signed state for a prescribed time or longer continued.Further, it has a function of notifying the input fault to the opposingdevice through the high-speed transmission path 0. Furthermore, it has afunction of interrupting the optical output to the high-speedtransmission path 0 according to the output control signal inputted fromthe control part 313-0.

[0306] The control part 313-0 has a function of monitoring the inputfault signals inputted from the low-speed transmission/reception parts312-0-1 to 312-0-4, the high-speed transmission/reception part 314-0 andthe DMUX part 310-0, and performing the output control of the low-speedtransmission/reception parts 312-0-1 to 312-0-4 and the output controlof the high-speed transmission/reception part 314-0.

[0307] Each of the low-speed transmission/reception parts 312-1-1 to312-1-4 in the multiplex device 305 is connected to the low-speedtransmission/reception parts 304-1-1 to 304-1-4 of the switching device306 via the low-speed transmission paths 301 b-1 to 304 b-1. Also, thelow-speed transmission/reception parts 312-1-1 to 312-1-4 are connectedto the MUX part 311-1 and the DMUX part 310-1, respectively, inside themultiplex device 305, while having a bi-directional conversion functionfor the optical signals on the low-speed transmission paths 301 b-1 to304 b-1 and the electric signals inside the multiplex device 305.Further, the low-speed transmission/reception parts 312-1-1 to 312-1-4have a function of monitoring the signal inputted from the low-speedtransmission paths 301 b-1 to 304 b-1, and notifying a fault in theinput signal to the control part 313-1 when there is a fault such as thenon-input-signed state being continued for a prescribed time or longer.Also, the low-speed transmission/reception parts 312-1-1 to 312-1-4 havea function of interrupting the optical output to the low-speedtransmission paths 301 b-1 to 304 b-1 according to the output controlsignal inputted from the control part 313-1.

[0308] The MUX part 311-1 multiplexes the signal inputted from thelow-speed transmission/reception parts 312-1-1 to 312-1-4 and outputsthe signals to the high-speed transmission/reception part 314-1. Also,it has a function of inserting a transmission path fault detectionpattern showing the fault by every channel according to an instructionfrom the control part 313-1.

[0309] The DMUX part 310-1 separates the signals which are inputted fromthe high-speed transmission/reception part 314-1 by channel unit andthen outputs it to the low-speed transmission/reception parts 312-1-1 to312-1-4 of the corresponding channel. Also, it has a function ofdetecting the transmission path fault detection pattern showing thefault of each channel and notifying the fault to the control part 313-1.

[0310] The high-speed transmission/reception part 314-1 is provided inbetween the MUX part 311-1, the DMUX part 310-1, and the high-speedtransmission path 1, and has a bi-directional conversion function forthe optical signal on the high-speed transmission path 1 and theelectric signal inside the device. Also, the high-speedtransmission/reception part 314-1 has a function of monitoring thesignal inputted from the high-speed transmission path 1 and notifyingthe input fault to the control part 313-1 when detecting the fault suchas the non-input-signed state being continued for a prescribed time orlonger. Further, it has a function of notifying the input fault to theopposing device through the high-speed transmission path 1. Furthermore,it has a function of interrupting the optical output to the high-speedtransmission path 1 according to the output control signal inputted fromthe control part 313-1.

[0311] The control part 313-1 has a function of monitoring the inputfault signals inputted from the low-speed transmission/reception parts312-1-1 to 312-1-4, the high-speed transmission/reception part 314-1 andthe DMUX part 310-1 and performing the output control of the low-speedtransmission/reception parts 312-1-1 to 312-1-4 and the output controlof the high-speed transmission/reception part 314-1.

[0312] Next, operation of the Example will be described.

[0313] It will be described by referring to the case where the system ofthe Example operates with the multiplex devices 302 and 304 being theactive systems and the duplex devices 303 and 305 being the standbysystem.

[0314] In FIG. 25, when the transmission fault path is detected in thehigh-speed transmission/reception part 309-0, the fault is notified tothe low-speed transmission/reception parts 312-0-1 to 312-0-4 throughthe control part 313-0, and the optical output to the low-speedtransmission paths 301 b-0 to 304 b-0 is interrupted. Thereby, thetransmission path fault is detected in the low-speedtransmission/reception parts 314-0-1 to 314-0-4 and is notified to thecontrol part 318. Thus, the selection system of SEL parts 315-1 to 315-4is switched from the 0-system to the 1-system. Also, by interrupting theoptical output of the low-speed transmission/reception parts 314-0-1 to314-0-4, the transmission path fault is notified in the reversedirection. Thereby, the transmission path fault is also detected in thelow-speed transmission/reception parts 304-0-1 to 304-0-4 of theswitching device 301. Thus, by the control of the control part 305, theselection system of the SEL parts 303-1 to 303-4 is switched from the0-system to the 1-system so that the transmission paths in bothdirections are switched from the 0-system to the 1-system.

[0315] Specific operation of each part is as follows.

[0316] In a normal state, the optical signal inputted from the low-speedline 301 a, after being converted to the electric signal in thelow-speed transmission/reception part 301-1, is copied in the COPY part302-1, and then converted to the optical signal in the low-speedtransmission/reception parts 304-0-1 and 304-1-1 to be outputted to theactive system low-speed transmission path 301 a-0 and the standby systemlow-speed transmission path 301 a-1. The operation of allotting theoptical signals from the low-speed line to the active system low-speedtransmission path 301 a-0 and to the standby system low-speedtransmission path 301 a-1 is performed for each of the low-speed lines301 a to 304 a, respectively.

[0317] In the multiplex devices 302 and 303, the data from eachlow-speed transmission path is multiplexed in the MUX parts 306-0, 306-1and output the data to the high-speed transmission path 0 and thehigh-speed transmission path 1. The multiplexed data are separated tothe data for each low-speed transmission path in the multiplex devices304, 305 and outputted to the low-speed transmission paths 301 b-0 and301 b-1.

[0318] In the switching device 306, the optical signal inputted from thelow-speed line 301 a is inputted to the low-speed transmission/receptionparts 314-0-1 and 314-1-1 and the data is transferred to the SEL part315-1. The control part 318, since the multiplex devices 302 and 304 areto be the operation system, controls the SEL part 315-1 to select thedata inputted from the low-speed transmission/reception part 314-0-1 viathe multiplex devices. The output of the SEL part 315-1 is transferredto the low-speed transmission/reception part 317-1 and is then convertedto the optical signal in the low-speed transmission/reception part 317-1to be outputted to the low-speed line 301 b. In the same manner, thedata in the reverse direction is copied in the COPY part 316-1 and thecopied data are then inputted to the low-speed transmission/receptionparts 304-0-1 and 304-1-1 of the switching device 301 through themultiplex devices 304, 302, and 305, 303. The data are inputted to theSEL part 303-1. However, the data inputted from the low-speedtransmission/reception part 304-0-1 is selected by the control of thecontrol part 305 to be outputted to the low-speed line 301 a. Asdescribed, it enables a bi-directional communication between thelow-speed line 301 a and the low-speed line 301 b.

[0319] Next, a case will be described in which, in the normal state, afault is generated in the high-speed transmission path 0 in thedirection from the duplex device 302 to the duplex device 304.

[0320] When there is a fault generated in the high-speed transmissionpath 0 which is the active system in the direction from the multiplexdevice 302 to the multiplex device 304, the high-speedtransmission/reception part 314-0 of the multiplex device 304 detectsthe input fault and notifies it to the control part 313-0. Also, theoptical output to the high-speed transmission path 0 is interrupted (oran input fault notified on signed is added to the output signal) therebyto notify the input fault to the multiplex device 302 through thetransmission path 0. The control part 313-0, upon receiving the inputfault notification, gives an instruction for interrupting the output tothe low-speed transmission/reception parts 312-0-1 to 312-0-4, and thelow-speed transmission/reception parts 312-0-1 to 312-0-4 therebyinterrupts the optical output to the low-speed transmission paths 301b-0 to 304 b-0.

[0321] In the low-speed transmission/reception parts 314-0-1 to 314-0-4of the switching device 306, the input fault is detected by theinterruption of the optical output to the low-speed transmission paths301 b-0 to 304 b-0 and is notified to the control part 318. The controlpart 318, upon receiving the input fault notification from the low-speedtransmission/reception parts 314-0-1 to 314-0-4, gives an instruction tothe SEL parts 315-1 to 315-4 to switch the selection system to the1-system when the input fault is not notified from the low-speedtransmission/reception parts 314-1-1 to 314-1-4 within a certain time.The SEL parts 315-1 to 315-4 switch the output data from the input dataof the low-speed transmission/reception parts 314-0-1 to 314-0-4 to theinput data of the low-speed transmission/reception parts 314-1-1 to314-1-4 according to the instruction from the control part 318.

[0322] In the multiplex device 302, the high-speedtransmission/reception part 308-0, when recognizing the sate of nooptical input from the high-speed transmission path 0 (or the inputfault notification from the high-speed transmission/reception part314-0), notifies the output fault to the control part 309-0. The controlpart 309-0 gives an instruction for interrupting the output to thelow-speed transmission/reception parts 305-0-1 to 305-0-4 according tothe output fault notification from the high-speed transmission/receptionpart 308-0. The low-speed transmission/reception parts 305-0-1 to305-0-4 interrupt the optical output to the low-speed transmission paths301 a-0 to 304 a-0 according to the instruction for interrupting theoutput. Thereby, the fault in the transmission path is notified to thelow-speed transmission/reception parts 304-0-1 to 304-0-4 of thereceiving switching device 301.

[0323] In the switching device 301, the input fault is detected in thelow-speed transmission/reception parts 304-0-1 to 304-0-4 and isnotified to the control part 305. The control part 305, when the inputfault is notified from the low-speed transmission/reception parts304-0-1 to 304-0-4, gives an instruction to the SEL parts 303-1 to 303-4to switch the selection system from the 0-system to the 1-system whenthe input fault is not notified from the low-speedtransmission/reception parts 304-1-1 to 304-1-4 within a certain time.The SEL parts 303-1 to 303-4 switch the output data from the input dataof the low-speed transmission/reception parts 304-0-1 to 304-0-4 to theinput data of the low-speed transmission/reception parts 304-1-1 to304-1-4 according to the instruction from the control part 305.

[0324] As described, due to the generation of fault in the high-speedline 0 a, switching of the transmission path is performed throughchanging the operation system from the 0-system to the 1-system.

[0325] Next, a case will be described in which, in a normal state, afault is generated in the low-speed transmission path 301 a-0 in thedirection from the switching device 301 to the duplex device 302.

[0326] When there is a fault generated in the low-speed transmissionpath 301 a-0 in the direction from the switching device 301 to themultiplex device 302, the multiplex device 302 detects the input faultin the low-speed transmission/reception path 305-0-1 and notifies theinput fault to the control part 309-0. The control part 309-0, uponreceiving the input fault notification from the low-speedtransmission/reception part 305-0-1, gives an instruction to the MUXpart 306-0 to generate the input fault detection pattern for thecorresponding channel to be inserted thereto. Upon receiving theinstruction, the MUX part 306-0 inserts the input fault detectionpattern instead of the data of the corresponding channel and the patternis multiplexed with the data of another channel to be transmitted to themultiplex device 304.

[0327] In the multiplex device 304, the input fault detection patterninserted by the MUX part 306-0 is detected in the DMUX part 310-0. TheDMUX part 310-0 notifies the fault of the corresponding channel to thecontrol part 313-0. The control part 313-0 outputs an instruction forinterrupting the output to the low-speed transmission/reception part312-0-1. The low-speed transmission/reception part 312-0-1 interruptsthe optical output to the low-speed transmission path 301 b-0 andnotifies the transmission path fault of the corresponding channel to theswitching device 306.

[0328] The low-speed transmission/reception part 314-0-1 of theswitching device 306, when detecting the transmission path fault,notifies the transmission path fault of the corresponding channel to thecontrol part 318. The control part 318 outputs an instruction forinterrupting the output to the low-speed transmission/reception part314-0-1, and outputs an instruction to the SEL part 315-1 for switchingthe low-speed transmission/reception part 314-1-0 to the low-speedtransmission part 314-1-1 when the transmission path fault notificationis not inputted from the low-speed transmission/reception part 314-1-1within a certain time. The SEL part 315-1 switches the selection systemsfrom the 0-system to the 1-system according to the switching instructionfrom the control part 318. The low-speed transmission/reception part314-0-1, upon receiving the instruction for interrupting the output,interrupts the optical output thereby to notify the transmission pathfault to the multiplex device 304.

[0329] The low-speed transmission/reception part 312-0-1 of themultiplex device 304, when detecting the transmission path fault fromthe low-speed transmission/reception part 314-0-1, notifies the fault tothe control part 313-0. The control part 313-0 then outputs aninstruction to the MUX part 311-0 to insert the transmission path faultdetection pattern. The MUX part 311-0 inserts the transmission pathfault detection pattern instead of the data of the corresponding channeland transmits it to the multiplex device 302 through the high-speedtransmission/reception part 314-0.

[0330] The DMUX part 307-0 of the multiplex device 302, when detectingthe transmission path fault detection pattern inserted to the channelwith transmission path fault, notifies the transmission path fault ofthe corresponding channel to the control part 309-0. The control part309-0, upon receiving the notification, outputs an instruction to thelow-speed transmission/reception part 305-0-1 for interrupting theoutput and the low-speed transmission/reception part 305-0-1 interruptsthe optical output to the low-speed transmission path 301 a-0.

[0331] The low-speed transmission/reception path 304-0-1 of theswitching device 301 detects the transmission path fault and notifiesthe transmission path fault to the control part 305. The control part305, after receiving the notification of the transmission path faultfrom the low-speed transmission/reception path 304-0-1, outputs aninstruction to the SEL part 303-1 for switching the system to thestandby system when the notification of the transmission path fault isnot received from the low-speed transmission/reception part 304-1-1 asthe standby transmission path within a certain time. The SEL part 303-1switches the selection systems from the 0-system to the 1-system. In themanner as described, switching of the 0-system transmission path to the1-system transmission path is performed when there is a transmissionpath fault is generated in the direction from the switching device 301to the multiplex device 304.

[0332] When the high-speed transmission path is SONET (SynchronousOptical Network)/SDH (Synchronous Digital Hierarchy), the alarm transferfunctions of the SONET/SDH can be utilized. Further, in the case where arelay is provided in the high-speed transmission path, the alarm can bealso transferred to the opposing device by the alarm transfer functionsof the SONET/SDH.

[0333]FIG. 26 to FIG. 28 are block diagrams for showing theconfiguration of another Example according to the present invention. TheExample will be described by referring to FIG. 26 to FIG. 28.

[0334] In the Example, as shown in FIG. 26 to FIG. 28, the switchingdevices 301 and 306 shown in FIG. 23 to FIG. 25 are replaced withswitching devices 301′ and 306′ having the inside structure differentfrom that of the switching devices 301 and 306. In the Example, as forthe structural parts of the switching devices 301′ and 306′, theoperation towards the outside of low-speed transmission/reception parts301-1′ to 301-4′, 304-0-1′ to 304-0-4′, 304-1-1′ to 304-1-4′, 317-1′ to317-4′, 314-0-1′ to 314-0-4′, 314-1-1′ to 314-1-4′ and control parts305′, 318′ are the same as that of the low-speed transmission/receptionparts 301-1 to 301-4, 304-0-1 to 304-0-4, 304-1-1 to 304-1-4, 317-1 to317-4, 314-0-1 to 314-0-4, 314-1-1 to 314-1-4 and the control parts 305,318, respectively. Thus, only the inside operation of each of theswitching devices 301′ and 306′ will be described below.

[0335] In the Example, a switching part 320 is provided in between thelow-speed transmission/reception parts 301-1′ to 301-4′ and thelow-speed transmission/reception parts 304-0-1′ to 304-0-4′, 304-1-1′ to304-1-4′ of the switching device 301′, and a switching part 321 isprovided in between the low-speed transmission/reception parts 317-1′ to317-4′ and the low-speed transmission/reception parts 314-0-1′ to314-0-4′, 314-1-1′ to 304-1-4′ of the switching device 306′.

[0336] Each of the switching parts 320 and 321 has twelve input portsand twelve output ports. Any of the output ports is not to be affectedby other output ports. The switching parts 320 and 321 are capable ofselecting one port out of all the input ports and of switching theselected port according to the selecting instruction from the controlpart 305′.

[0337] In the switching parts 320 and 321 at the initial state, theoutput port 1 is connected to the input port 5, the output port 2 to theinput port 6, the output port 3 to the input port 7, the output port 4to the input port 8, the output port 5 to the input port 1, the outputport 6 to the input port 2, the output port 7 to the input port 3, theoutput port 8 to the input port 4, the output port 9 to the input port1, the output port 10 to the input port 2, the output port 11 to theinput port 3, and the output port 12 to the input port 4.

[0338] In the normal state, the data inputted from the low-speed line301 a is converted to electric signal in the low-speedtransmission/reception part 301-1′, copied in the switching part 320,and then outputted to the low-speed transmission paths 301 a-0 and 301a-1 from the low-speed transmission/reception parts 304-0-1′ and304-1-1′. The data is then multiplexed with data from another low-speedtransmission path in the multiplex devices 302, 303 and then outputtedto the high-speed transmission path 0 and the high-speed transmissionpath 1. Subsequently, the data are separated from the data from anothertransmission path in the multiplex devices 304, 305 and outputted to thelow-speed transmission paths 301 b-0 and 301 b-1. The data inputted tothe low-speed transmission/reception parts 314-0-1′, 314-1-1′ aretransferred to the switching part 321 and the data inputted from thelow-speed transmission/reception part 314-0-1′ is selected to beoutputted to the low-speed line 301 b. In the same manner, the data inthe reverse direction is copied in the switching part 321, and inputtedto the low-speed transmission/reception parts 304-0-1′, 304-1-1′ of theswitching device 301′ through the multiplex devices 304, 302, and themultiplex devices 305, 303. The data are then inputted to the switchingpart 320 and the data inputted from the low-speed transmission/receptionpart 304-0-1′ is selected to be outputted to the low-speed line 301 a.In the manner as described, it enables a bi-directional communicationbetween the low-speed line 301 a and the low-speed line 301 b.

[0339] Next, operation of the Example in the case where, in the normalstate, there is a fault generated in the high-speed transmission path 0in the direction from the multiplex device 302 to the multiplex device304 will be described.

[0340] When there is a fault generated in the high-speed transmissionpath 0 in the direction from the multiplex device 302 to the multiplexdevice 304, the high-speed transmission/reception part 314-0 of themultiplex device 304 detects the input fault and notifies the controlpart 313-0. Also, it notifies the input fault to the multiplex device302 via the high-speed transmission path 0 through interrupting theoptical output to the high-speed transmission path 0 (or adding an inputfault notification signal to the output signal).

[0341] The control part 313-0 of the duplex device 304, upon receivingthe notification of the input fault, outputs an instruction to thelow-speed transmission/reception parts 312-0-1 to 312-0-4 forinterrupting the output. The low-speed transmission/reception parts312-0-1 to 312-0-4, upon receiving the instruction for interrupting theoutput from the control part 313-0, notifies the fault in thetransmission path to the low-speed transmission/reception parts 314-0-1to 314-0-4 of the switching device 306′ as the receiving device byinterrupting the optical output to the low-speed transmission paths 301b-0 to 304 b-0.

[0342] The low-speed transmission/reception parts 314-0-1′ to 314-0-4′of the switching device 306′ detect the input fault and notify thecontrol part 318′. The control part 318′, upon receiving notification ofthe input fault from the low-speed transmission/reception parts 314-0-1′to 314-0-4′, outputs an instruction to the output ports 1 to 4 of theswitching part 321 for switching the selection ports to the input ports9 to 12 when the input fault is not notified from the low-speedtransmission/reception parts 314-1-1′ to 314-1-4′ within a certain time.The switching part 321 switches the output data of the output ports 1 to4 from the data of the low-speed transmission/reception parts 314-0-1′to 314-0-4′ to the data of the low-speed transmission/reception parts314-1-1′ to 314-1-4′ according to the instruction from the control part318′.

[0343] On the other hand, in the multiplex device 302, the high-speedtransmission/reception part 308-0, upon receiving the notification ofthe input fault, notifies the input fault to the control part 309-0. Thecontrol part 309-0, upon receiving the notification of the input fault,outputs an instruction to the low-speed transmission/reception parts305-0-1 to 305-0-4 for interrupting the output. The low-speedtransmission/reception parts 305-0-1 to 305-0-4, when receiving theinstruction for interrupting the output, interrupts the optical outputto the low-speed transmission paths 301 a-0 to 304 a-0 thereby to notifythe fault in the transmission path to the low-speedtransmission/reception parts 304-0-1′ to 304-0-4′ of the switchingdevice 301′ as the receiving device.

[0344] The low-speed transmission/reception parts 304-0-1′ to 304-0-4′of the switching device 301′ detect the input fault and notify thecontrol part 305′. The control part 305′, upon receiving notification onthe input fault from the low-speed transmission/reception parts 304-0-1′to 304-0-4′, outputs an instruction to the output ports 1 to 4 of theswitching part 320 for switching the selection ports to the input ports9 to 12 when the input fault is not notified from the low-speedtransmission/reception parts 304-1-1′ to 304-1-4′ within a certain time.The switching part 320 switches the output data from the data of thelow-speed transmission/reception parts 304-0-1′ to 304-0-4′ to the dataof the low-speed transmission/reception parts 304-1-1′ to 304-1-4′according to the instruction from the control part 305′.

[0345] In the manner as described above, switching of the transmissionpaths is performed by changing the operation system from the 0-systemtransmission path to the 1-system transmission path when there is afault generated in the high-speed line 0 a.

[0346] Next, operation of the Example in the case where, in the normalstate, there is a fault generated in the low-speed transmission path 310a-0 in the direction from the switching device 301′ to the multiplexdevice 302 will be described.

[0347] When there is a fault generated in the low-speed transmissionpath 301 a-0 in the direction from the switching device 301′ to themultiplex device 302, the low-speed transmission/reception path 305-0-1detects the input fault and notifies the input fault to the control part309-0. The control part 309-0, upon receiving the input faultnotification from the low-speed transmission/reception part 305-0-1,gives an instruction to the MUX part 306-0 to generate the input faultdetection pattern for the corresponding channel to be multiplexedtherewith. The MUX part 306-0 inserts the input fault detection patterninstead of the data of the corresponding channel and the pattern ismultiplexed with the data of another channel. The input fault detectionpattern inserted in the MUX part 306-0 is transmitted to the multiplexdevice 304.

[0348] In the multiplex device 304, the DMUX part 310-0 detects theinput fault detection pattern. The DMUX part 310-0 then notifies thefault of the corresponding channel to the control part 313-0. Thecontrol part 313-0 outputs an instruction for interrupting the output tothe low-speed transmission/reception part 312-0-1. The low-speedtransmission/reception part 312-0-1 interrupts the optical output to thelow-speed transmission path 301 b-0 thereby to notify the transmissionpath fault of the corresponding channel to the switching device 306′.

[0349] The low-speed transmission/reception part 314-0-1′ of theswitching device 306′ when detecting the transmission path fault,notifies the transmission path fault of the corresponding channel to thecontrol part 318′. The control part 318′ outputs an instruction to thelow-speed transmission/reception part 314-0-1′ for interrupting theoutput, and outputs an instruction to the output port 1 of the switchingpart 321 for switching the selection port to the input port 9 when thetransmission path fault notification is not inputted from the low-speedtransmission/reception part 314-1-1′ within a certain time. Theswitching part 321 switches the selection port of data according to theswitching instruction from the control part 318′. The low-speedtransmission/reception part 314-0-1′, upon receiving the instruction forinterrupting the output from the control part 318′, interrupts theoptical output thereby to interrupt the transmission path fault to themultiplex device 304.

[0350] The low-speed transmission/reception part 312-0-1 of themultiplex device 304, when detecting the transmission path fault,notifies the fault to the control part 313-0. The control part 313-0then outputs an instruction to the MUX part 311-0 to insert thetransmission path fault detection pattern. The MUX part 311-0 insertsthe transmission path fault detection pattern instead of the data of thecorresponding channel and transmits it to the multiplex device 302through the high-speed transmission/reception part 314-0.

[0351] The DMUX part 307-0 of the multiplex device 302, when detectingthe transmission path fault detection pattern and the transmission pathfault channel, notifies the transmission path fault of the correspondingchannel to the control part 309-0. The control part 309-0 outputs aninstruction to the low-speed transmission/reception part 305-0-1 forinterrupting the output, and the low-speed transmission/reception part305-0-1 interrupts the optical output to the low-speed transmission path301 a-0.

[0352] The low-speed transmission/reception path 304-0-1′ of theswitching device 301′ detects the transmission path fault and notifiesthe transmission path fault to the control part 305′. The control part305′, after receiving the notification of the transmission path faultfrom the low-speed transmission/reception path 304-0-1′, outputs aninstruction to the output port 1 of the switching part 320 for switchingthe selection port to the input port 9 when the notification on thetransmission path fault is not received from the low-speedtransmission/reception part 304-1-1′ as the standby system transmissionpath within a certain time. The output port 1 of the switching part 320switches data from the data of the low-speed transmission/reception part304-0-1 to the data of the low-speed transmission/reception part304-1-1. In the manner as described, switching of the 0-systemtransmission path to the 1-system transmission path is performed whenthere is a transmission path fault generated in the direction from theswitching device 301′ to the multiplex device 304.

[0353]FIG. 29 to FIG. 31 show an example using the system of theabove-described Example. It is an example of the system comprising threeuser lines with transmission duplex service and two user lines with thesingle transmission path service.

[0354] The users of the transmission path duplex service (the user usingthe low-speed transmission lines 301 a to 303 a and the low-speedtransmission lines 301 b to 303 b) are stored in the multiplex devicevia the switching devices 301′ and 304′, while the users of the singletransmission service (the user of the low-speed lines 304 a, 305 a, 304b, and 305 b) are directly stored in the multiplex device withoutpassing through the switching devices. Specifically, the low-speed lines304 a, 305 a, 304 b and 305 b are connected to the low-speedtransmission/reception parts 305-0-4, 305-1-4, 312-0-4, and 312-1-4.Other configuration is the same as that of the Example shown in FIG. 26to FIG. 28. The configuration described here is also applicable to theExample shown in FIG. 26 to FIG. 28.

[0355] The users of the transmission path duplex service can avoid to bein the incommunicable state when there is a fault generated in eitherthe 0-system transmission path or the 1-system transmission path.However, for the users of the single transmission path service, theservice is to be down when there is a fault generated in thetransmission line the users belong to. Thus, the single transmissionpath service can be provided at a lower price than that of thetransmission path duplex system.

[0356] The present invention is formed in the manner as described.Therefore, it can achieve the effects as described below. The firsteffect is, in the communication system such as Ethernet using datacommunication protocol in which no alarm transfer function is defined,to be able to improve the reliability through duplicating the relaytransmission paths and switching the transmission paths in a short timewhen a fault is generated. This can be achieved since, when the fault inthe transmission path is detected, the generation of fault is notifiedto the up and down direction of the communication using the transmissionpath, and also the fault can be detected in a short time through using amethod of interrupting the optical output to the optical transmissionpath in each device as the method for notifying the fault.

[0357] The second effect is that a flexible service can be provided andthe device can be effectively utilized. The reason is for this is that,since the switching function for duplicating the transmission path isseparated from the multiplex deice, it is possible that the lines of theusers using the duplex service of the transmission path are connected tothe multiplex device through the switching device, and the lines of theusers (single service) who do not use the duplex service are directlyconnected to the multiplex device. Therefore, the number of users storedin the system can be increased. For example, if there is a multiplexdevice for multiplexing four channels and the number of the users usingthe transmission path duplex service is three, the total number of theusers using the transmission path duplex service or the single serviceis to be four in the multiples system in which the switching function isunified, and to be five in the system in which the switching function isseparated (FIG. 29 to FIG. 31).

[0358] The third effect is that the switching device can be connected todevices with various types of communication protocols. The reason isthat the switching is performed through detecting the loss of optical orelectrical signals so that the switching device does not depend on thecommunication protocol or the transmission medium.

[0359] The fourth effect is that it is capable of avoiding theincommunicable state when there are faults generated in a plurality ofpoints. The reason is that, although a plurality of lines are stored inthe switching device, it has a configuration in which each line can beindividually switched so that the generation of double-faults can berestored. For example, when a fault is being generated in the low-speedtransmission path 301 a-0 and the low-speed line 301 a is in operationby the 1-system, if a fault is simultaneously generated on the low-speedtransmission path 302 a-1 side, the low-speed line 302 a can be operatedby the 0-system. Therefore, the operation can be continued with no cutin the line.

[0360] By applying the multiplex communication system of the presentinvention described above to Ethernet, it becomes possible to monitorthe network in a communication system which performs communicationbetween computers using Ethernet. Next, the advantages of the case inwhich the multiplex communication system of the present invention isapplied to the communication system using Ethernet will be described indetail by making comparison to the conventional example.

[0361] Conventionally, when using Ethernet for communication betweencomputers (especially, personal computers), supervisory monitoring ofnetwork as the Internet has not been performed. This is due to the factthat the Internet is originally provided on the basis of “Best EffortService” (a service that can be used when the band is available, but noguarantee for the band and the quality). However, there has been themovement for using the Internet as the basic system network and in sucha case, it is necessary to guarantee the band and the quality. Forexample, it is necessary to achieve the protection function whichrestores the fault in the line by switching the line to the standbytransmission path when the fault is generated in the transmission pathin order to guarantee the quality.

[0362] In the duplex method of the transmission device performed by SDH(Synchronous Digital Hierarchy), the signal inputted from the terminalis branched and multiplexed to be connected to the present system pathand the standby system path, and in the selection device for selectingthe present system path and the standby system path, the present systempath is switched to the standby system path when there is a fault in thepresent system path.

[0363]FIG. 37 is a block diagram showing the configuration of aconventional duplex device. A branching circuit 1202 branches a signalS1201 into signals S1204 and S1205. A selection circuit 1205 selectseither one of a selected signal S1206 or a selected signal S1207 andoutput it as a signal S1212. The branching circuit 1202 and theselection circuit 1205 are provided in between the Ethernet terminal andEthernet terminating device. The selection circuit 1205 selects thepresent system signal (for example, S1206) and, when there is a fault inthe present system, selects the standby system signal (for example,S1207).

[0364] At the time of a fault generated in the transmission path, whendata from the terminal is terminated once and is capsulized by atechnique such as GFP (Generic Framing Procedure) or the like to betransferred through the relay section, data link control between theterminals cannot be performed. Therefore, the generation of fault isnotified to the opposing device by defining the alarm transfer frame.

[0365] At present, the Internet has not been used as the basic systemnetwork as described above, so that switching to the standbytransmission path is not performed.

[0366] In Ethernet, normality of the paths including the Ethernetterminals and the Ethernet terminating devices is judged based onwhether or not the link between the Ethernet terminals and the Ethernetterminating devices is established.

[0367] In the case where the above-described SDH switching method isapplied as it is to the switching method of Ethernet path, when thepresent system is normal, the Ethernet terminating device can receivesignals from the Ethernet terminals by the auto-negotiation between thestandby system Ethernet terminals and the Ethernet terminating device.However, the auto-negotiation cannot be completed since the signalstransmitted from the device itself are not connected to Ethernetterminals. As a result, link between the standby system Ethernetterminals and the Ethernet terminating device cannot be established.Therefore, the control device for performing switching of the presentsystem and the standby system recognizes as if there is a faultgenerated in the standby system path even though the standby system pathis in a normal state. Thus, the switching is not performed.

[0368] An object of the present invention is, in the case where theabove-described Ethernet is used as the basic system network, to achievethe Ethernet redundant method and the system which can properly performswitching to the standby system through judging the normal state whenthe standby system Ethernet path is normal.

[0369] In order to achieve the foregoing object, the Ethernet redundantsystem according to the present invention comprises: a plurality ofpaths formed in an Ethernet terminating device for connecting betweenEthernet terminals in duplex; and a duplex switch provided between theboth Ethernet terminals and a plurality of the paths for connecting theEthernet terminals to the Ethernet terminating device forming a presentsystem path, and connecting the Ethernet terminating device forming astandby system path in such a manner that the output to be an input, andfor switching the present system path to the standby system path whenthere is a fault in the present system path. In this case, a relay maybe provided in the paths.

[0370] Also, the duplex switch may comprise first to third inputterminals and output terminals to be capable of connecting each inputterminal and output terminal at will.

[0371] Also, the duplex switch may comprise: a first branching circuitand a first selection circuit provided for the Ethernet terminals; and asecond and a third branching circuits and a second and a third selectioncircuits provided, respectively, for each Ethernet terminating deviceforming the present system and the standby system paths. The firstbranching circuit may branch a signal from the Ethernet terminals andoutput the branched signals to the second and third selection circuits;each of the second and third branching circuits may branch a signal fromthe corresponding Ethernet terminating device and output the branchedsignals to the first, the second and the third selection circuits; thefirst selection circuit may select a signal from the branching circuitprovided for the Ethernet terminating device forming a present systempath and output the signal to the Ethernet terminal; the secondselection circuit may select a signal from the first branching circuitand outputs the signal to the corresponding Ethernet terminating device;and the third selection circuit may select a signal from the thirdbranching circuit and outputs the signal to the corresponding Ethernetterminating device.

[0372] Another Ethernet redundant system according to the presentinvention comprises: a plurality of paths formed in an Ethernetterminating device for connecting between Ethernet terminals inN-multiplex; and an N-multiplex switch provided between the bothEthernet terminals and a plurality of the paths for connecting theEthernet terminals to the Ethernet terminating device forming a presentsystem path, and connecting the Ethernet terminating device forming astandby system path in such a manner that the output to be an input, andfor switching the present system path to the standby system path whenthere is a fault in the present system path. In this case, a relay isprovided in the paths.

[0373] The N-multiplex switch may comprise a plurality of inputterminals and output terminals to be capable of connecting each inputterminal and output terminal at will.

[0374] Also, the N-multiplex switch may comprise: a branching circuitand a selection circuit provided for the Ethernet terminals; and aplurality of branching circuits and selection circuits provided,respectively, for each Ethernet terminating device forming a pluralityof paths. The branching circuit provided for the Ethernet terminal maybranch a signal from the Ethernet terminal and outputs the branchedsignals to a plurality of the selection circuits provided for eachEthernet terminating device; each of a plurality of the branchingcircuits provided for each Ethernet terminating device may branch asignal from the corresponding Ethernet terminating device and output thebranched signals to the selection circuit provided for the Ethernetterminal and the selection circuit provided for the correspondingEthernet terminating device; the selection circuit provided for theEthernet terminal may select a signal from the branching circuitprovided for the Ethernet terminating device forming a present systempath and output the signal to the Ethernet terminal; the selectioncircuit provided for the Ethernet terminal forming the present systempath may select a signal from the branching circuit provided for theEthernet terminal and outputs the signal to the corresponding Ethernetterminating device; and the selection circuit provided for the Ethernetterminating device forming the standby system path may select a signalfrom the branching circuit provided for the corresponding Ethernetterminating device and outputs the signal to the corresponding Ethernetterminating device.

[0375] The Ethernet redundant system according to the present inventioncomprises: a plurality of paths formed in an Ethernet terminating devicefor connecting between Ethernet terminals in duplex; and a duplex switchprovided between the both Ethernet terminals and a plurality of thepaths for connecting the Ethernet terminals to the Ethernet terminatingdevice forming a present system path, and connecting the Ethernetterminating device forming a standby system path in such a manner thatthe output to be an input, and for switching the present system path tothe standby system path when there is a fault in the present systempath.

[0376] In this case, a switch may be used as the duplex switch,comprising first to third input terminals and output terminals andcapable of connecting each input terminal and output terminal at will.

[0377] Further, as the duplex switch, a switch may be used comprising: afirst branching circuit and a first selection circuit provided for theEthernet terminal; and a second and third branching circuits and asecond and a third selection circuits provided, respectively, for eachEthernet terminating device forming the present system and the standbysystem paths, in which the first branching circuit branches a signalfrom the Ethernet terminal and output the branched signals to the secondand third selection circuits; each of the second and third branchingcircuits branch a signal from the corresponding Ethernet terminatingdevice and output the branched signals to the first selection circuitand the second and thirds selection circuits; the first selectioncircuit selects a signal from the branching circuit provided for theEthernet terminating device forming a present path and output the signalto the Ethernet terminal; the second selection circuit selects a signalfrom the first branching circuit and outputs the signal to thecorresponding Ethernet terminating device; and the third selectioncircuit selects a signal from the third branching circuit and outputsthe signal to the corresponding Ethernet terminating device.

[0378] Another Ethernet redundant method according to the presentinvention comprises the steps of: providing a plurality of paths formedin an Ethernet terminating device for connecting in between Ethernetterminals in N-multiplex; and providing an N-multiplex switch providedbetween the both Ethernet terminals and a plurality of the paths forconnecting the Ethernet terminals to the Ethernet terminating deviceforming a present system path, and connecting the Ethernet terminatingdevice forming a standby system path in such a manner that the output tobe an input, and for switching the present system path to the standbysystem path when there is a fault in the present system path.

[0379] In this case, as the N-multiplex switch, a switch comprising aplurality of input terminals and output terminals and capable ofconnecting each input terminal and output terminal at will may be used.

[0380] Further, as the N-multiplex switch, a switch may be usedcomprising: a branching circuit and a selection circuit provided for theEthernet terminals; and a plurality of branching circuits and selectioncircuits provided for each Ethernet terminating device forming aplurality of paths, respectively, in which the branching circuitprovided for the Ethernet terminating device branches a signal from theEthernet terminals and outputs the branched signals to a plurality ofthe selection circuits provided for each Ethernet terminating device;each of a plurality of the branching circuit provided for each Ethernetterminating device branch a signal from the corresponding Ethernetterminating device and output the branched signals to the selectioncircuit provided for the Ethernet terminal and the selection circuitsprovided for the corresponding Ethernet terminating device; theselection circuit provided for the Ethernet terminal selects a signalfrom the branching circuit provided for the Ethernet terminating deviceforming a present system path and output the signal to the Ethernetterminal; the selection circuit provided for the Ethernet terminatingdevice forming the present system path selects a signal from thebranching circuit provided for the Ethernet terminal and outputs thesignal to the corresponding Ethernet terminating device; and theselection circuit provided for the corresponding Ethernet terminatingforming the standby system path device selects a signal from thebranching circuit provided for the corresponding Ethernet terminatingdevice and outputs the signal to the corresponding Ethernet terminatingdevice.

[0381] In the present invention formed as described, in the. Ethernetterminating devices forming the standby system path, output and inputare connected in return form. Therefore, it looks as if it is connectedto the Ethernet terminals and the link is established. As a result, whenswitching the path from the present system to the standby system, thestandby system path is judged as normal and the switching is performed.

[0382] Next, an Example of the present invention will be described byreferring to the drawings. The Example, as shown in FIG. 32, comprisesEthernet terminals 411, 412, duplex devices 421, 422, and Ethernetterminating terminals 431, 432, 441, 442.

[0383] The Ethernet terminals 411 and 412 are connected to the duplex421, 422 which are connected each other via the Ethernet terminatingdevice 431, 432, 441 and 442. The Ethernet terminating device 431 andthe Ethernet terminating device 432 are positioned opposing to eachother and the Ethernet terminal 441 and the Ethernet terminal 442 arepositioned opposing to each other. The Ethernet terminal 411 and theEthernet terminal 412 are connected via a first path going through theduplex devices 421, 422, the Ethernet terminating terminals 431, 432 andvia a second path going through the duplex device 421, 422, Ethernetterminating terminals 441, 442.

[0384] Link establishing control in Ethernet is performed between theEthernet terminals 411, 412 and the Ethernet terminating devices 431,432, 441, 442. In between the Ethernet terminating devices 431, 432,441, and 442, data is capsulized by GFP or the like to be transferredafter terminating MAC (Media Access Control) layer of Ethernet.

[0385] The Ethernet terminating devices 431, 432, 441 and 442 performalarm transfer to the opposing Ethernet terminating devices when a faultis generated. The Ethernet terminating devices, upon receiving the alarmnotification, notifies the fault notification to the duplex devices 421and 422 through interrupting the output signals to the duplex devices421 and 422.

[0386] The duplex devices 421 and 422, as shown in FIG. 33, comprise a3×3 switching circuit 401. With the 3×3 switching circuit 401, itbecomes possible to output an input signal S401 as either an outputsignal S404 or an output signals 405 at will, or to output either aninput signal S406 or an input signal S407 as an output signal S412 atwill.

[0387] The switching operation of the 3×3 switching circuit 401 of theExample is performed by control devices (not shown) provided in theduplex devices 421 and 422. The control devices detect the signal statepassing through the 3×3 switching circuit 401 and switches the 3×3switching circuit 401 according to the state.

[0388] In the case of the Example as shown in FIG. 32, the duplex device411 is connected to the Ethernet terminal 412 via the input signal S401and the output signal S412. It is also connected to the Ethernetterminating device 431 via the input signal S406 and the output signalS404, and connected to the Ethernet terminating device 441 via the inputsignal S407 and the output signal S405. Further, the duplex device 422is connected to the Ethernet terminal 412 via the input signal S401 andthe output signal S412. It is also connected to the Ethernet terminatingdevice 432 via the input signal S406 and the output signal S404, andconnected to the Ethernet terminating device 442 via the input signalS407 and the output signal S405.

[0389] Next, operation of the Example will be described. When the paththrough the Ethernet terminating devices 431, 432 is used as the presentsystem and the path through the Ethernet terminating devices 441, 442 isused as the standby system, in the duplex device 421, the input signalS401 from the Ethernet terminal 411 is switched in the 3×3 switchingcircuit 401 to the output signal S404 for the Ethernet terminatingdevice 431, the input signal S406 from the Ethernet terminating device431 to the output signal S412 for the Ethernet terminal 411, and theinput signal S407 from the Ethernet terminating device 441 to the outputsignal S405 for the Ethernet terminating device 441.

[0390] In the same manner, in the duplex device 422, the input signalS401 from the Ethernet terminal 412 is switched in the 3×3 switchingcircuit 401 to the output signal S404 for the Ethernet terminatingdevice 432, the input signal S406 from the Ethernet terminating device432 to the output signal S412 for the Ethernet terminal 412, and theinput signal S407 from the Ethernet terminating device 442 to the outputsignal S405 for the Ethernet terminating device 442.

[0391] By providing the above-described connection state, the linkbetween the Ethernet terminal 411 and the Ethernet terminating device431 is established, and the link between the Ethernet terminal 412 andthe Ethernet terminating device 432 is also established. Also, it looksas if the Ethernet terminating devices 441, 442 are connected to theEthernet terminals 411, 412 so that the link is established.

[0392] Now, operation of the case where a fault is generated in thepresent path going through the Ethernet terminating devices 431 and 432will be described. It will be described by referring to a case, as anexample, where a fault is generated in the transmission path connectedfrom the duplex device 421 to the Ethernet terminating device 431.

[0393] Due to a generating of the fault, the Ethernet terminating device431 becomes incommunicable of data transmission and the auto-negotiationfunction operates thereby downing the link between with the Ethernetterminal 411 as the link partner. Also, the Ethernet terminating device431 performs the alarm transfer to the opposing Ethernet terminatingdevice 432.

[0394] Upon detecting the alarm notification transmitted from theEthernet terminating device 431, the Ethernet terminating device 432interrupts the signal outputted to the duplex device 422. The duplexdevice 422, upon detecting the non-input signal state from the Ethernetterminating device 432, switches the connection of the 3×3 switchingcircuit 401 thereby to connect the standby system path going through theEthernet terminating devices 441, 442 to the Ethernet terminal 412 afterconfirming that the input signal from the standby system Ethernetterminating device 442 is not interrupted. Specifically, the inputsignal S401 from the Ethernet terminal 412 is switched to the outputsignal S405 for the Ethernet terminating device 442, the input signalS407 from the Ethernet terminating device 442 to the output signal S412for the Ethernet terminal 412, and the input signal S406 from theEthernet terminating device 432 to the output signal S404 for theEthernet terminating device 432.

[0395] Before the path switching is performed in the duplex device 422,the signal outputted from the Ethernet terminating circuit 432 to theduplex device 422 is interrupted so that the signal inputted to theEthernet terminal 412 is also to be interrupted. Thus, the link of theEthernet terminating device 412 is in a down-state. In the Ethernetterminating device 412, the auto-negotiation function operates when thelink becomes down thereby to start the operation for establishing thelink between the link partner. Until the switching is performed in theduplex device 422, the link partner is the Ethernet terminating device432. Thus, the incommunicable state continues and the link is notestablished. When the switching of the path is performed in the duplexdevice 422, the link partner of the Ethernet terminal 412 changes to theEthernet terminating device 442. Thereby, the signal is connected and,by the auto-negotiation function, the link is established therebetween.

[0396] The Ethernet terminating device 431 interrupts the signaloutputted to the duplex device 421 upon detecting the transmission pathfault. The duplex device 421, upon detecting the non-input signal statefrom the Ethernet terminating device 431, switches the connection of the3×3 switching circuit 401 thereby to make the standby system of Ethernetterminating device 441 the link partner of the Ethernet terminal 411. Atthis time, the operation of the duplex circuit 421 and the Ethernetterminal 411 is the same as that of the duplex device 422 and theEthernet terminal 412 described above.

[0397] When the fault continues even after the connection of the 3×3switching circuit 401 in the duplex device 421, 422 is switched, theEthernet terminating device 431 continues to detect the fault whilecontinuing to interrupts the output signal to the duplex device 421 andto transmit the alarm transfer to the Ethernet terminating device 432.Thereby, the duplex device 421 continues to detect the non-input signalstate from the Ethernet terminating device 431 and the duplex device 422continues to detect the non-input signal state from the Ethernetterminating device 432.

[0398] When the fault is restored, the Ethernet terminating device 431cancels the fault detection and cancels the interruption of the outputsignal to the duplex device 421. At the same time, it cancels the alarmtransfer to the Ethernet terminating device 432. The Ethernetterminating device 432 cancels the interruption of the output signal tothe duplex device 422 when the alarm notification is not detected.

[0399] The duplex devices 421 and 422 detect that the initial presentsystem path going through the Ethernet terminating devices 431, 432 hasrestored to the normal state based on the fact that the output signalfrom the Ethernet terminating devices 431, 432 to the duplex devices421, 422 has returned to be normal. Also, the Ethernet terminatingdevice 431 continues the auto-negotiation while the link is down.However, when the fault is restored, it looks as if it is communicablebetween with the Ethernet terminating device 411 and the link isreestablished. It is the same in the Ethernet terminating device 432.

[0400] Although not shown in FIG. 32, a relay for performing along-distance transmission may be provided between the Ethernetterminating devices 431, 441, and the Ethernet terminating devices 432,442.

[0401] In the Example formed in the manner as described, even in thecase where the link between the present system Ethernet terminal and theEthernet terminating device is established, it is possible to establishthe link between the standby system Ethernet terminating device. Thus,the duplex device performing the switching can judge whether or not thestandby system path is in the normal state and switches the Ethernetpath to the standby system in the normal state when there is a faultgenerated in the present system.

[0402] Next, another Example of the present invention will be described.In the Example, the configuration of the duplex devices 421, 422 isprovided different from that of the duplex devices 421, 422 shown inFIG. 32. However, other configuration is the same as that shown in FIG.32.

[0403]FIG. 34 is a block diagram showing the configuration of the duplexdevices 421 and 422 of the Example. The duplex devices 421 and 422 ofthe Example comprise a first branching circuit 402, a second branchingcircuit 403, a third branching circuit 404, a first selection circuit405, a second selection circuit 406 and a third selection circuit 407.

[0404] The first branching circuit 402 branches the input signal S401into the signal S402 and the signal S403 and outputs the signals to thesecond selection circuit 406 and the third selection circuit 407,respectively. The second branching circuit 403 branches the input signalS406 into the signal S408 and the signal S409 and outputs the signals tothe first selection circuit 405 and the second selection circuit 406,respectively. The third branching circuit 407 branches the input signalS407 into the signal S410 and the signal S411 and outputs the signals tothe first selection circuit 405 and the third selection circuit 407,respectively. The first selection circuit 405 selects either one of theinputted signals S408 or S410 and output it as the signal S412. Thesecond selection circuit 406 selects either one of the inputted signalsS402 or S409 and output it as the signal S404. The third selectioncircuit 407 selects either one of the inputted signals S403 or S411 andoutput it as the signal S405.

[0405] The selection of the signals in the first to third selectioncircuits 405 to 407 of the Example is performed by control devices (notshown) provided in the duplex devices 421 and 422. The control devicedetects the state of the signals passing through the first to thirdselection circuits 405 to 407 and performs the switching of the first tothird selection circuits 405 to 407 according to the state.

[0406] When the path through the Ethernet terminating devices 431, 432is used as the present system and the path through the Ethernetterminating devices 441, 442 is used as the standby system, in theduplex device 421, the input signal S401 from the Ethernet terminal 411is switched in the second selection circuit 406 to the output signalS404 for the Ethernet terminating device 431, the input signal S406 fromthe Ethernet terminating device 431 is switched in the first selectioncircuit 405 to the output signal S412 for the Ethernet terminal 411, andthe input signal S407 from the Ethernet terminating device 441 isswitched in the third selection circuit 407 to the output signal S405for the Ethernet terminating device 441.

[0407] In the same manner, in the duplex device 422, the input signalS401 from the Ethernet terminal 412 is switched in the second selectioncircuit 406 to the output signal S404 for the Ethernet terminatingdevice 432, the input signal S406 from the Ethernet terminating device432 is switched in the first selection circuit 405 to the output signalS412 for the Ethernet terminal 412, and the input signal S407 from theEthernet terminating device 442 is switched in the third selectioncircuit 407 to the output signal S405 for the Ethernet terminatingdevice 442.

[0408] By providing the above-described connection state, the linkbetween the Ethernet terminal 411 and the Ethernet terminating device431 is established, and the link between the Ethernet terminal 412 andthe Ethernet terminating device 432 is also established. Also, it looksas if the Ethernet terminating devices 441, 442 are connected to theEthernet terminals 411, 412 so that the link is established.

[0409] Now, operation of the case where a fault is generated in thepresent system path through the Ethernet terminating devices 431 and 432will be described. It will be described by referring to a case, as anexample, where a fault is generated in the transmission path connectedfrom the duplex device 421 to the Ethernet terminating device 431.

[0410] Due to a generation of the fault, the Ethernet terminating device431 becomes incommunicable of data transmission and the auto-negotiationfunction operates thereby downing the link between with the Ethernetterminal 411 as the link partner. Also, the Ethernet terminating device431 performs the alarm transfer to the opposing Ethernet terminatingdevice 432.

[0411] Upon detecting the alarm notification transmitted from theEthernet terminating device 431, the Ethernet terminating device 432interrupts the signal outputted to the duplex device 422. The duplexdevice 422, upon detecting the non-input signal from the Ethernetterminating device 432, switches the connection thereby to connect thestandby system path going through the Ethernet terminating devices 441,442 to the Ethernet terminal 412 after confirming that the input signalfrom the standby system Ethernet terminating device 442 is notinterrupted. Specifically, the input signal S401 from the Ethernetterminal 412 is switched in the third selection circuit 407 to theoutput signal S405 for the Ethernet terminating device 442, the inputsignal S407 from the Ethernet terminating device 442 is switched in thefirst selection circuit 405 to the output signal S412 for the Ethernetterminal 412, and the input signal S406 from the Ethernet terminatingdevice 432 is switched in the second selection circuit 406 to the outputsignal S404 for the Ethernet terminating device 432.

[0412] Before the path switching is performed in the duplex device 422,the signal outputted from the Ethernet terminating circuit 432 to theduplex device 422 is interrupted so that the signal inputted to theEthernet terminal 412 is also to be interrupted. Thus, the link of theEthernet terminating device 412 is in the down-state. In the Ethernetterminating device 412, the auto-negotiation function operates when thelink becomes down thereby to start the operation for establishing thelink with the link partner. Until the switching is performed in theduplex device 422, the link partner is the Ethernet terminating device432. Thus, the incommunicable state continues and the link is notestablished. When the switching of path is performed in the duplexdevice 422, the link partner of the Ethernet terminal 412 changes to theEthernet terminating device 442. Thereby, the signal is connected and,by the auto-negotiation function, the link is established therebetween.

[0413] The Ethernet terminating device 431 interrupts the signaloutputted to the duplex device 421 upon detecting the transmission pathfault. The duplex device 421, upon detecting the non-input signal statefrom the Ethernet terminating device 431, switches the connectionthereby to make the standby system Ethernet terminating device 441 thelink partner of the Ethernet terminal 411. At this time, the operationof the duplex device 421 and the Ethernet terminal 411 is the same asthat of the duplex device 422 and the Ethernet terminal 412 describedabove.

[0414] When the fault continues even after the connection in the duplexdevice 421, 422 is switched, the Ethernet terminating device 431continues to detect the fault while continuing to interrupt the outputsignal to the duplex device 421 and to transmit the alarm transfer tothe Ethernet terminating device 432. Thereby, the duplex device 421continues to detect the non-input signal state from the Ethernetterminating device 431 and the duplex circuit 422 continues to detectthe non-input signal state from the Ethernet terminating device 432.

[0415] When the fault is restored, the Ethernet terminating device 431cancels the fault detection and cancels the interruption of the outputsignal to the duplex device 421. At the same time, it cancels the alarmtransfer to the Ethernet terminating device 432. The Ethernetterminating device 432 cancels the interruption of the output signal tothe duplex device 422 when the alarm notification is not detected.

[0416] The duplex devices 421 and 422 detect that the initial presentsystem path going through the Ethernet terminating devices 431, 432 hasrestored to the normal state based on the fact that the output signalfrom the Ethernet terminating devices 431, 432 to the duplex devices421, 422 has returned to be normal. Also, the Ethernet terminatingdevice 431 continues the auto-negotiation while the link is down.However, when the fault is restored, it looks as if it is communicablebetween with the Ethernet terminal 411 and the link is reestablished. Itis the same also in the Ethernet terminating device 432.

[0417] In the Examples described above, the paths between the Ethernetterminals are duplicated. However, it may have a configuration with thenumber of the standby systems being increased to be N-multiplexed (N isinteger of 2 or larger), in which the N-multiplex switch connects theEthernet terminal to the Ethernet terminating device for forming thepresent system path and connects the Ethernet terminating device forforming the standby system path in such a manner that the output is tobe the input, and switches the path to the standby system when there isa fault generated in the present system path.

[0418] The N-multiplex switching, as in that of the Example shown inFIG. 32, may comprise a plurality of input and output terminals to becapable of connecting each input terminal and output terminal at will.Further, as the Example shown in FIG. 33, it may comprise a branchingcircuit and a selection circuit provided for the Ethernet terminal, anda plurality of branching circuits and selection circuits provided,respectively, for each Ethernet terminating device forming a pluralityof paths, in which: the branching circuit provided for the Ethernetterminal branches the signal from the Ethernet terminal and outputs thesignals to a plurality of the selection circuits provided for eachEthernet terminating device; each of a plurality of the branchingcircuit provided for each Ethernet terminating device branches thesignal from the corresponding Ethernet terminating device and outputsthe signals to the selection circuit provided for the Ethernet terminaland the selection circuit provided for the corresponding Ethernetterminating device; the selection circuit provided for the Ethernetterminal selects the signal from the branching circuit provided for theEthernet terminating device forming the present path and outputs it tothe Ethernet terminal; and the selection circuit provided for theEthernet terminating device for forming the present system path selectsthe signal from the branching circuit provided for the Ethernet terminaland outputs it to the corresponding Ethernet terminating device and theselection circuit provided for the Ethernet terminating device forforming the standby system path selects the signal from the branchingcircuit provided for the corresponding Ethernet terminating device andoutputs it to the corresponding Ethernet terminating device.

[0419] In the present invention formed in the manner as described, linkbetween the Ethernet terminal and the Ethernet terminating device isestablished by the auto-negotiation function regardless of the systems(present or standby). Therefore, it is possible to judge whether or notthe standby system path is in the normal state and when the standbysystem is confirmed to be normal, switching of the Ethernet path can beexecuted in the case of a fault generated in the present system.

What is claimed is:
 1. A line switching system in a multiplexcommunication system, comprising a plurality of terminal devices and aplurality of line switching devices, wherein: at least one terminaldevice is connected to one line switching device and one line switchingdevice is connected to another line switching device via a present lineand a standby line; one terminal device is connected to another terminaldevice prescribed beforehand to be capable of communication via a lineswitching device and a present line so that communication is achievedusing a protocol without a line switching function; and the standby lineis a line replaceable with the present line, wherein: the line switchingdevice comprises: a fault detection unit for detecting generation of afault through checking whether or not a recognizable signal is detectedfrom a line within a prescribed time; and a line switching unit for,when the fault detection unit detects generation of a fault in thepresent line, switching the present line with the fault detected by thefault detection unit to the standby line which can be replaced with thepresent line thereby to perform communication between the terminaldevice and another terminal device prescribed beforehand.
 2. The lineswitching system as claimed in claim 1, wherein the line switching unitswitches the line after a switching protection time has passed from thedetection of a fault by the fault detection unit.
 3. The line switchingsystem as claimed in claim 2, further comprising a fault notificationunit for notifying generation of fault to another line switching devicewhen the generation of fault is detected in the fault detection unit. 4.The line switching system as claimed in claim 3, wherein: the lines usedfor connecting each device are full duplex lines composed of atransmission line and a reception line; and the fault notification unitcomprises: a function of, when a fault is detected in one of the linesout of the full duplex lines by the fault detection unit, notifying thefault using the other line of the full duplex lines.
 5. The lineswitching system as claimed in claim 3, wherein the fault notificationunit comprises a function of notifying a fault by periodically repeatinginterruption of signal output and transmission of a link down patternfor downing the link in a protocol; wherein in a period in theperiodical repeat, time for transmitting the link down pattern is setlonger than time for interrupting output.
 6. The line switching systemas claimed in claim 1, further comprising at least one transmissiondevice capable of achieving a long distance communication between aterminal device and another terminal device, which is provided in eachof the present line and the standby line in a line switching device;wherein the transmission device comprises: a transmission-side faultdetection unit for detecting generation of a fault when a recognizablesignal is not detected from the line within a prescribed time or byreceiving notification of a fault generation; and a transmission-sidefault notification unit for notifying the generation of fault when thetransmission-side fault detection unit detects the generation of fault.7. The line switching system as claimed in claim 6, wherein thetransmission-side notification unit has a function of: notifying thegeneration of fault to a line switching device by interrupting signaloutput; and notifying to a transmission device by periodicallytransmitting a reception fault notification packet and a link downnotification packet; wherein in a period in the periodical transmissionof the notification, time for transmitting the link down notificationpacket is set longer than time for transmitting the reception faultnotification packet.
 8. The line switching system as claimed in claim 7,wherein detection of a fault through receiving notification of the faultgeneration transmitted from the transmission-side fault detection unitis achieved by receiving the reception fault notification packet or/andreceiving a link down notification packet.
 9. The line switching systemas claimed in claim 1, wherein: when the fault detection unit detects afault generated in between a terminal device and a line switching devicenearest to the terminal device, the fault notification unit transmits alink down pattern to a transmission line.
 10. A line switching method ina multiplex communication system, wherein: at least one terminal deviceis connected to one line switching device and one line switching deviceis connected to another line switching device via a present line and astandby line; one terminal device is connected to another terminaldevice prescribed beforehand to be capable of communication via a lineswitching device and a present line so that communication is achievedusing a protocol without a line switching function; and the standby lineis a line replaceable with the present line, comprising: a faultdetection step for detecting generation of a fault through checkingwhether or not a recognizable signal is detected from a connected linewithin a prescribed time; and a line switching step for, when the faultdetection step detects generation of a fault in the present line,switching the present line with the fault detected by the faultdetection unit to the standby line which can be replaced with thepresent line thereby to perform communication between the terminaldevice and another terminal device prescribed beforehand.
 11. The lineswitching method as claimed in claim 10, wherein the line switchingstep, the line is switched after a switching protection time has passedfrom the detection of a fault in the fault detection step.
 12. The lineswitching method as claimed in claim 11, further comprising a faultnotification step for notifying generation of a fault to another lineswitching device when the generation of a fault is detected in the faultdetection step.
 13. The line switching method as claimed in claim 12,wherein: the lines used for connecting each device are full duplex linescomposed of a transmission line and a reception line; and in the faultnotification step: when a fault is detected in one of the lines out ofthe full duplex lines by the fault detection step, the fault is notifiedusing the other line of the full duplex lines.
 14. The line switchingmethod as claimed in claim 12, wherein: in the fault notification step,a fault is notified by periodically repeating interruption of signaloutput and transmission of a link down pattern for downing the link in aprotocol; and in a period in the periodical repeat, time fortransmitting the link down pattern is set longer than time forinterrupting output.
 15. The line switching method as claimed in claim10, wherein at least one transmission device capable of achieving a longdistance communication between a terminal device and another terminaldevice is further provided in each of the present line and the standbyline in a line switching device; comprising: a transmission-side faultdetection step for detecting generation of a fault by the transmissiondevice when a recognizable signal is not detected from the line within aprescribed time or by receiving a notification of a fault generation;and a transmission-side fault notification step for notifying thegeneration of fault when the generation of fault is detected in thetransmission-side fault detection step.
 16. The line switching method asclaimed in claim 15, wherein: in the transmission-side faultnotification step, a line switching device is notified by interruptionof signal output; a transmission device is notified by periodicaltransmission of a reception fault notification packet and a link downnotification packet; wherein in a period in the periodical transmissionof notification, time for transmitting the link down notification packetis set longer than time for transmitting the reception faultnotification packet.
 17. The line switching method as claimed in claim16, wherein detection of a fault through receiving notification of thefault generation in the transmission-side fault detection step isachieved by receiving the reception fault notification packet or/andreceiving a link down notification packet.
 18. The line switching methodas claimed in claim 10, wherein, when a fault generated in between aterminal device and a line switching device nearest to the terminaldevice is detected in the fault detection step, a link down pattern istransmitted to a transmission line in the fault notification step. 19.An optical transmission switching device in a multiplex communicationsystem, comprising: a replaceable optical module capable of performingphotoelectric conversion or electric-optic conversion on inputted data;a CDR circuit being provided in correspondence with the data from theoptical module for reproducing data and clock at a timing according to aset rate; and a device information judging circuit for judging deviceinformation of the optical module through reading out type information,that is, information about the types of interface of the optical moduleand a transmission code in the interface, and for setting the rate ofthe CDR circuit through discriminating the interface rate.
 20. Anoptical transmission switching device cin a multiplex communicationsystem comprising: a first replaceable optical module capable ofperforming photoelectric conversion on inputted data; a first CDRcircuit for reproducing data and clock from the data from the firstoptical module at a timing according to a set rate; a first deviceinformation judging circuit for judging device information of the firstoptical module through reading out type information, that is,information about the types of interface of the first optical module anda transmission code in the interface, and for setting the rate of thefirst CDR circuit through discriminating the interface rate; a branchingcircuit for branching data which is waveform-shaped by the first CDRcircuit into a plurality of systems; a plurality of second CDR circuitsfor reproducing, respectively, a plurality of data and clocks which arebranched by the branching circuit at a timing according to a set rate; aplurality of replaceable second optical modules for performing,respectively, electric-optic conversion on a plurality of data which arewaveform-shaped by the second CDR circuits; and a plurality of seconddevice information judging circuits for judging respectively, deviceinformation of a plurality of the second optical modules through readingout type information, that is, information about the types of interfaceof a plurality of the second optical modules and a transmission code inthe interface and for setting, respectively, the rate of a plurality ofthe second CDR circuits through discriminating the interface rate,respectively.
 21. An optical transmission switching device in amultiplex communication system comprising: a plurality of firstreplaceable optical module which is performing photoelectric conversionon inputted data each other; a plurality of first CDR circuits forreproducing, respectively, data and clock from a plurality of the firstoptical modules at a timing according to a set rate; a plurality offirst device information judging circuits for judging, respectively,device information of a plurality of the first optical modules,respectively, through reading out type information, that is, informationabout the types of interface of a plurality of the first optical modulesand a transmission code in the interface and for setting, respectively,the rate of a plurality of the first CDR circuits through discriminatingthe interface rate; a selection circuit for selecting a system which canreceive an effective data through recognizing presence of a plurality ofsystems of data which are waveform-shaped by a plurality of the firstCDR circuits; a second CDR circuit for reproducing data and clock of thesystem selected by the selection circuit at a timing according to a setrate; a second optical module for performing electric-optic conversionon data which is waveform-shaped by the second CDR circuit; and a seconddevice information judging circuit for judging device information of thesecond optical module through reading out type information, that is,information about the types of interface of the second optical moduleand a transmission code in the interface, and for setting the rate ofthe second CDR circuit through discriminating the interface rate,respectively.
 22. An optical transmission switching device in amultiplex communication system comprising: a plurality of firstreplaceable optical modules, each capable of performing photoelectricconversion on inputted data; a plurality of first CDR circuits forreproducing, respectively, data and clock from a plurality of the firstoptical modules at a timing according to a set rate; a plurality offirst device information judging circuits for judging, respectively,device information of a plurality of the first optical modules throughreading out type information, that is, information about the types ofinterface of a plurality of the first optical modules and a transmissioncode in the interface and for setting, respectively, the rate of aplurality of the first CDR circuits through discriminating the interfacerate; a switching circuit for outputting data on a plurality of lineswhich are waveform-shaped by a plurality of first CDR circuits to arecipient determined based on the line setting set beforehand; a linesetting circuit for performing line-switching on the switching circuitbased on a setting from outside; a plurality of second CDR circuits forreproducing, respectively, data and clock on a plurality of linesoutputted from the switching circuit at a timing according to a setrate; a second optical module for performing electric-optic conversionon data which is waveform-shaped by the second CDR circuit; and aplurality of second device information judging circuits for judging,respectively, device information of a plurality of the second opticalmodules through reading out type information, that is, information aboutthe types of interface of a plurality of the second optical modules anda transmission code in the interface and for setting, respectively, therate of a plurality of the second CDR circuits through discriminatingthe interface rate.
 23. A multiplex communication system, comprising aswitching device for duplicating data on a plurality of transmissionpaths thereby to distribute the data to an active system transmissionpath and a standby system transmission path; and a multiplex deviceprovided on each of the active system transmission path and the standbysystem transmission path for multiplexing data which are distributed bythe switching device and transmitted via the transmission paths, whereina control part is provided in each of the switching device and themultiplex device, and each of the control part together switches thetransmission path from the active system to the standby system upondetecting a fault in the transmission path based on a state that no datasigned is transmitted via each transmission path.
 24. The multiplexcommunication system as claimed in claim 23, wherein the multiplexdevice comprises: a plurality of low-speed transmission/reception partsconnected to a switching device; a multiplex part for multiplexing datareceived in the low-speed transmission/reception part; a high-speedtransmission/reception part for outputting multiplex data multiplexed bythe multiplex part to another opposing multiplex device; a separationpart for separating the multiplex data from the opposing multiplexdevice received in the high-speed transmission/reception part andoutputting the separated data to a plurality of the low-speedtransmission/reception parts; and a control part for controllingoperation of each part, wherein each of the low-speedtransmission/reception parts and the high-speed transmission/receptionpart notify an input fault to the control part and interrupt output ofsignal when input of signal from the transmission path connected to theswitching device and the opposing multiplex device is interrupted for aprescribed time or longer; and the control part, upon receiving thenotification, interrupts the output signal of the slow-speedtransmission/reception parts or the high-speed transmission/receptionpart to which the fault has not been notified.
 25. The multiplexcommunication system as claimed in claim 24, wherein the switchingdevice comprises: a plurality of first low-speed transmission/receptionparts connected to a plurality of transmission paths, respectively; aplurality of second and third low-speed transmission/reception partsconnected to the multiplex device provided on the active system andstandby system transmission paths, respectively, corresponding to aplurality of the low-speed transmission/reception parts; acopy/selection part provided in between the first low-speedtransmission/reception parts and the second and third low-speedtransmission/reception parts, for copying data from the first low-speedtransmission/reception parts and outputting the data to the second andthird low-speed transmission/reception parts, and for selecting dataeither from the second or third low-speed transmission/reception partand outputting it to the first low-speed transmission/reception parts;and a control part for controlling operation of each part, wherein eachof the second and third low-speed transmission/reception part notifiesan input fault to the control part when input of signal from thetransmission path connected to the multiplex device is interrupted for aprescribed time or longer; and the control part, upon receiving thenotification, makes the copy/selection part select the data from thesecond low-speed transmission/reception part in a normal state and, whennotified of an input fault from the second low-speedtransmission/reception part, makes the copy/selection part select thedata from the third low-speed transmission/reception part afterconfirming that there is no notification about an input fault from thethird low-speed transmission/reception part for a prescribed time orlonger.
 26. The multiplex communication system as claimed in claim 25,wherein the copy/selection part comprises: a copy part for copying datafrom the first low-speed transmission/reception parts to output the datato the second and third low-speed transmission/reception parts; and aselection part for selecting the data either from the second or thirdlow-speed transmission/reception part to output it to the firstlow-speed transmission/reception parts.
 27. The multiplex communicationsystem as claimed in claim 25, wherein the copy/selection part is aswitch with a plurality of input/output ports.
 28. An Ethernet redundantsystem, comprising: a plurality of paths formed by Ethernet terminatingdevice for connecting between Ethernet terminals in duplex; and a duplexswitch provided between the both Ethernet terminals and a plurality ofthe paths for connecting the Ethernet terminals to the Ethernetterminating device forming a present system path, and connecting theEthernet terminating device forming a standby system path in such amanner that the output to be an input, and for switching the presentsystem path to the standby system path when there is a fault in thepresent system path.
 29. The Ethernet redundant system as claimed inclaim 28, wherein the paths are provided with a relay.
 30. The Ethernetredundant system as claimed in claim 28, wherein: the duplex switchcomprises first to third input terminals and output terminals, and iscapable of connecting each input terminal and output terminaloptionally.
 31. The Ethernet redundant system as claimed in claim 28,wherein the duplex switch comprises: a first branching circuit and afirst selection circuit provided for the Ethernet terminals; and asecond and a third branching circuits and a second and a third selectioncircuits provided, respectively, for each Ethernet terminating deviceforming the present system and the standby system paths, wherein thefirst branching circuit branches a signal from the Ethernet terminalsand output the branched signals to the second and third selectioncircuits; each of the second and third branching circuits branches asignal from the corresponding Ethernet terminating device and output thebranched signals to the first, the second and the third selectioncircuits; the first selection circuit selects a signal from thebranching circuit provided for the Ethernet terminating device forming apresent system path and output the signal to the Ethernet terminal; thesecond selection circuit selects a signal from the first branchingcircuit and outputs the signal to the corresponding Ethernet terminatingdevice; and the third selection circuit selects a signal from the thirdbranching circuit and outputs the signal to the corresponding Ethernetterminating device.
 32. An Ethernet redundant system comprising: aplurality of paths formed in an Ethernet terminating device forconnecting between Ethernet terminals in N-multiplex; and an N-multiplexswitch provided between the both Ethernet terminals and a plurality ofthe paths, for connecting the Ethernet terminals to the Ethernetterminating device forming a present system path, and connecting theEthernet terminating device forming a standby system path in such amanner that the output to be an input, and for switching the presentsystem path to the standby system path when there is a fault in thepresent system path.
 33. The Ethernet redundant system as claimed inclaim 32, wherein the paths are provided with a relay.
 34. The Ethernetredundant system as claimed in claim 32, wherein: the N-multiplex switchcomprises a plurality of input terminals and output terminals, and iscapable of connecting each input terminal and output terminaloptionally.
 35. The Ethernet redundant system as claimed in claim 32,wherein the N-multiplex switch comprises: a branching circuit and aselection circuit provided for the Ethernet terminals; and a pluralityof branching circuits and selection circuits provided, respectively, foreach Ethernet terminating device forming a plurality of paths, whereinthe branching circuit provided for the Ethernet terminal branches asignal from the Ethernet terminal and outputs the branched signals to aplurality of the selection circuits provided for each Ethernetterminating device; each of a plurality of the branching circuitsprovided for each Ethernet terminating device branch a signal from thecorresponding Ethernet terminating device and output the branchedsignals to the selection circuit provided for the Ethernet terminal andthe selection circuit provided for the corresponding Ethernetterminating device; the selection circuit provided for the Ethernetterminal selects a signal from the branching circuit provided for theEthernet terminating device forming a present system path and output thesignal to the Ethernet terminal; the selection circuit provided for theEthernet terminal forming the present system path selects a signal fromthe branching circuit provided for the Ethernet terminal and outputs thesignal to the corresponding Ethernet terminating device; and theselection circuit provided for the Ethernet terminating device formingthe standby system path selects a signal from the branching circuitprovided for the corresponding Ethernet terminating device and outputsthe signal to the corresponding Ethernet terminating device.
 36. AnEthernet redundant method comprising steps of: forming a plurality ofpaths in an Ethernet terminating device for connecting between Ethernetterminals in duplex; and providing a duplex switch between the bothEthernet terminals and a plurality of the paths, for connecting theEthernet terminals to the Ethernet terminating device forming a presentsystem path, and connecting the Ethernet terminating device forming astandby system path in such a manner that the output to be an input, andfor switching the present system path to the standby system path whenthere is a fault in the present system path.
 37. The Ethernet redundantmethod as claimed in claim 36, wherein: as the duplex switch, a switch,comprising first to third input terminals and output terminals andcapable of connecting each input terminal and output terminaloptionally, is used.
 38. The Ethernet redundant method as claimed inclaim 36, wherein, the method uses a duplex switch comprising: a firstbranching circuit and a first selection circuit provided for theEthernet terminal; and a second and third branching circuits and asecond and a third selection circuits provided, respectively, for eachEthernet terminating device forming the present system and the standbysystem paths, wherein the first branching circuit branches a signal fromthe Ethernet terminal and output the branched signals to the second andthird selection circuits; each of the second and third branchingcircuits branch a signal from the corresponding Ethernet terminatingdevice and output the branched signals to the first selection circuitand the second and thirds selection circuits; the first selectioncircuit selects a signal from the branching circuit provided for theEthernet terminating device forming a present path and output the signalto the Ethernet terminal; the second selection circuit selects a signalfrom the first branching circuit and outputs the signal to thecorresponding Ethernet terminating device; and the third selectioncircuit selects a signal from the third branching circuit and outputsthe signal to the corresponding Ethernet terminating device.
 39. AnEthernet redundant method comprising the steps of: providing a pluralityof paths formed by Ethernet terminating device for connecting in betweenEthernet terminals in N-multiplex; and providing an N-multiplex switchbetween the both Ethernet terminals and a plurality of the paths, forconnecting the Ethernet terminals to the Ethernet terminating deviceforming a present system path, and connecting the Ethernet terminatingdevice forming a standby system path in such a manner that the output tobe an input, and for switching the present system path to the standbysystem path when there is a fault in the present system path.
 40. TheEthernet redundant method as claimed in claim 39, wherein: as theN-multiplex switch, a switch, comprising a plurality of input terminalsand output terminals and capable of connecting each input terminal andoutput terminal optimally, is used.
 41. The Ethernet redundant method asclaimed in claim 39, wherein, the method uses an N-multiplex switchcomprising: a branching circuit and a selection circuit provided for theEthernet terminals; and a plurality of branching circuits and selectioncircuits provided for each Ethernet terminating device forming aplurality of paths, respectively, wherein the branching circuit providedfor the Ethernet terminal branches a signal from the Ethernet terminalsand outputs the branched signals to a plurality of the selectioncircuits provided for each Ethernet terminating device; each of aplurality of the branching circuit provided for each Ethernetterminating device branch a signal from the corresponding Ethernetterminating device and output the branched signals to the selectioncircuit provided for the Ethernet terminal and the selection circuitsprovided for the corresponding Ethernet terminating device; theselection circuit provided for the Ethernet terminal selects a signalfrom the branching circuit provided for the Ethernet terminating deviceforming a present system path and output the signal to the Ethernetterminal; the selection circuit provided for the Ethernet terminalforming the present system path selects a signal from the branchingcircuit provided for the Ethernet terminal and outputs the signal to thecorresponding Ethernet terminating device; and the selection circuitprovided for the corresponding Ethernet terminating device selects asignal from the branching circuit provided for the correspondingEthernet terminating device and outputs the signal to the correspondingEthernet terminating device.